The problem I see with using half the aileron width for flaps is, the chord of the ailerons (legth fron to back) is relatively small because the ailerons are full wing width. Cutting that in half span wise will substantially reduce the effectiveness of the ailerons. Flaps on that plane are also likely to be pretty ineffectual, especially if they're that same narrow chord.

Now, if you were to say, double the chord of the 'new' flaps and ailerons, it might make an interesting modification. Would it be worth it? Not to me, because it also entails major modifications to the wing. (I'd want to double up on a couple of the ribs at least to compensate for the increased flight loads of the larger surfaces.)

Rather than go through all that, spend a few dollars a buy a Sig Kadet Senior kit. That plane will slow down to near walking speed without having to make modifications.

Good luck,
Dennis-