No, moral acts are definitely not beautiful for Kant. They are objects of respect (as consistent through all works on practical philosophy by Kant), which is to some extend similar, but actually more a kind of the sublime. By virtue of judging it as a case of morality, you exclude the mere reflection on the intuition that is kantian beauty simply because of the alteration of the object of reflection.
But YES, there has to be "an affinity" between morality and beauty. Actually, Kant states in the quote (which I edited into the question, admittedly) that the positivity (and feeling of universalisability) of the feeling of beauty actually is grounded in it being the symbol of morality.
In order to fully answer the question, there have to be three aspects adressed, while the points 2 and 3 some kind of lay ground for the statements of the first one, as section 59 is rather late in the book and many aspects are just reformulations and clarifications of former arguments and conclusions:
What does Kant actually write in the mentioned section?
How are the sublime and the beautiful destinguished?
How is respect (for the moral law) destinguished from both of them?
Regarding § 59 of the Critique of the Power of Judgement
First, please consider the title of this section: On beauty as a symbol of
That does make two points to consider: First, we are speaking here of the opposite direction: It is not the moral act that is beautiful, it is the beauty that is a symbol of morality. Secondly, what does this actually mean (for Kant)?
Here, Kant is quite clear:
All hypotyposis (presentation, subjecto sub adspectum), as making
something sensible, is of one of two kinds: either schematic, where to
a concept grasped by the understanding the corresponding intuition is
given a priori; or symbolic, where to a concept which only reason can
think, and to which no sensible intuition can be adequate, an intuition
is attributed with which the power of judgment proceeds in a way
merely analogous to that which it observes in schematization, i.e., it is
merely the rule of this procedure, not of the intuition itself, and thus
merely the form of the reflection, not the content, which corresponds
to the concept. (Critique of the Power of Judgement, § 59, Ak. 5:351, Cambridge Edition p. 225)
The main point here is that beauty is to some extend similar/linked to morality (which HAS a schematism, see second critique), but not in the sense of a necessary schematism, but only in a symbolic manner, because there are only the 'form of the reflection' together with some other things that are to some extend equal. And he extensively explains in what sense they are equal and where the analogy ends afterwards:
We will adduce several
aspects of this analogy, while at the same time not leaving unnoticed
1) The beautiful pleases immediately (but only in reflecting intuition, not, like morality, in the concept). 2) It pleases without any
interest (the morally good is of course necessarily connected with an interest, but not with one that precedes the judgment on the satisfaction, but rather with one that is thereby first produced). 3) The freedom of the imagination (thus of the sensibility of our faculty) is represented in the judging of the beautiful as in accord with the
lawfulness of the understanding (in the moral judgment the freedom of
the will is conceived as the agreement of the latter with itself in accordance with universal laws of reason). 4) The subjective principle for
judging of the beautiful is represented as universal, i.e., valid for
everyone, but not as knowable by any universal concept (the objective
principle of morality is also declared to be universal, i.e., knowable for
all subjects, and at the same time also for all actions of one and the
same subject, yet by means of a universal concept). Hence the moral
judgment is not only capable of determinate constitutive principles, but
is also possible only by means of the grounding of its maxims on these
principles and their universality. (Critique of the Power of Judgement, § 59, Ak. 5:353-4, Cambridge Edition p. 227-8)
Regarding the sublime as destinct from beauty
In section 23, Kant destinguishes the sublime and the beauty. The main difference is stated as followed:
The most important and intrinsic difference between the sublime
and the beautiful, however, is this: that if, as is appropriate, we here
consider first only the sublime in objects of nature (that in art is, after
all, always restricted to the conditions of agreement with nature),
natural beauty (the self-sufficient kind) carries with it a purposiveness
in its form, through which the object seems as it were to be predetermined for our power of judgment, and thus constitutes an object of
satisfaction in itself, whereas that which, without any rationalizing,
merely in apprehension, excites in us the feeling of the sublime, may
to be sure appear in its form to be contrapurposive for our power of
judgment, unsuitable for our faculty of presentation, and as it were
doing violence to our imagination, but is nevertheless judged all the
more sublime for that. (Critique of the Power of Judgement, § 23, Ak. 5:245, Cambridge Edition p. 129)
In section 27, still in the chapter regarding the sublime, Kant explicitely states:
The feeling of the inadequacy of our capacity for the attainment of
an idea that is a law for us is respect. (Critique of the Power of Judgement, § 27, Ak. 5:257, Cambridge Edition p. 140)
As we speak here of an inadequacy ('unsuitability' in the quote above) of our capacity, respect clearly is a case of the sublime. Beware: Point 3) in the examination of the analogy speaks of "accordance" rather than inadequacy and rightfully so. Because while we are definately inadequate in our capacity to match the foundational moral law (as we are not able to fully act in accordance to it everytime and categorically), we are able to imagine an accordance in particular cases (which is the reason for our moral feeling). There is no contradiction here!
Regarding respect as some kind of 'link' between beauty and the sublime and destinguished from each of them
In section 29 Kant writes something that can be understood as some kind of the basis for the possibility of beauty as symbol of morality. First of all, he destinguishes by the object:
In relation to the feeling of pleasure an object is to be counted either among
the agreeable or the beautiful or the sublime or the (absolutely) good (iucun
dum, pulchrum, sublime, honestum). (Critique of the Power of Judgement, § 29, Ak. 5:266, Cambridge Edition p. 149)
And after some clarification, he concludes:
If one draws the result from the exposition thus far of the two kinds of
aesthetic judgment, the outcome would be the following brief explanations:
That is beautiful which pleases in the mere judging (thus not by means of the sensation of sense nor in accordance with a concept of the understanding). From this it follows of itself that it must please without any interest.
That is sublime which pleases immediately through its resistance to the
interest of the senses.
Both, as explanations of aesthetically universally valid judging, are related
to subjective grounds, namely on the one hand to those of sensibility, as it is purposive in behalf of the contemplative understanding, on the other, in opposition to those, as purposive for the ends of practical reason; and yet both,
united in the same subject, are purposive in relation to the moral feeling. The
beautiful prepares us to love something, even nature, without interest; the
sublime, to esteem it, even contrary to our (sensible) interest. (Critique of the Power of Judgement, § 29, Ak. 5:267, Cambridge Edition p. 150-1)
That means that 'respect' has some aspects of beauty (also see first point), but does not express the feeling of an accordance with our capacities, but a shortfalling (as finite beings), and is therefore some kind of the sublime. But the main difference to both of them is the objectiveness of the (grounds of the) judgement, as the object of beauty as well as the sublime is different (intuitions/representations vs. morality as a concept, see 1) in the remarks on the analogy). They are therefore destinct, but purposive, as they each acquaint with one of what is both part of the moral feeling, i.e. respect.