Meaning of "make trim of"

Solution 1:

I'm not sure if the following self-answer is correct, but here's what I found out.

The original Greek is this:

γενομενος εβουληθην των παρ ημιν αἱρέσεων ἐμπειρίαν λαβειν

My Greek is pretty poor, but I think γίγνομαι=to become, and βούλομαι=to wish, ἐμπειρία=experience, practice. Maybe αἱρέσεων is some other koine usage of a word that has to do with import duties. So anyway, it seems like he wants to become experienced. The translation by Thackeray on the right-hand side across from the Greek is "gain personal experience," which seems to match this word-by-word translation.

So it seems like the idea that Whiston is trying to represent in English with "make trim of" is something that means "gain personal experience." If it's a reference to tailoring, then it probably does mean "try on for size."