I went through the same questions to get an old Royal 25 that I had on the bench with no muffler. The OS 32 size muffler fits perfect (I think it came off a 32 SX). I don't have any docs on the motor, but there is a guy on eBay who sells crank cases and piston/sleeves for the Royal 25 an other Royal engines. I bought the parts and they arrived brand new in a couple days. I paid $25 for a replacement crank case and the piston/sleeve.

Jason