I've seen a bunch of different lengths for the cartridge cases, and tried several. One of the things discovered is that with the shortened 7.62 Nagant cases, 1.145" will work well with the .32-caliber semi-wadcutters; on this rifle at least that case length will not work with the 120-grain original style bullet, it's just too long and the bullet is contacting the rifling before you can seat the cartridge all the way into the chamber.
So tried it with a 1.140; better, but still a bit too long for that bullet. Looks like, for these, probably 1.135 will be the best overall. 'Probably' because I'll have to shorten a few so we can try them, and that'll be a few days.
Cartridge case summation:
.32-20 cases can be successfully converted, and work well; they are a bit delicate because the case walls are so thin, but since you only have to resize about the first 1/3(for some uses won't have to) they'll last for many firings. The Nagant cases are much stronger, and- because of the thicker case walls- you don't have to resize them to get a firm grip on the bullet heel, just expand the mouth a touch to allow them to start in easily.
Length will vary, apparently a lot. I've read of some that won't work with cases over 1.125", others considerably longer. This one seems to work well with 1.135" cases and below(have used some all the way down to 1.120" with good results). If you wind up with one of these that's been rechambered for .32-20 cases, you can use them as-is.
I suspect that, after a few uses, it might be a good idea to anneal the case mouths of the Nagant brass; it's stiff enough that if you don't they might start cracking at the mouth if you don't. We'll see.