US$75 is a good price for the 38cc. I'd say go for it. It should convert no different than all the 33-42cc Poulans. You'll indeed have to figure out a way to mount the magneto pickup on the engine, but the carb insulator is a simple bolt-on unlike the 46cc.

Bigbird1, what's your setup on the 46cc (muffler, ign, etc.)?