I have not tried to fit them on Perry bodies, but as you can scale them down I think it's not a problem (I've asked JJG to print me some at 100% and some at 90% of normal size to fit on "real" 1/56 minis). As WG models are bulkier than the Perry ones, I will try a 90/95 % size...
Resin is good, but a little fragile (especially on thin pieces like the barrels of guns).
Just ask JJG boss. He's a nice guy, and will answer all your qestions.