How big is the ridge on top of the piston? As I recall, the baffle (stunt) version has a baffle about 1/8" high.
As for the G.21, look in the little circle in the V on the side. That tells the displacement. If it is a .35, it is an old combat engine that you can sell for enough to buy a good modern stunt engine. Running one of those in a Magician would be like using a vintage Ferrari for a school bus: it's not well suited for the job and would be more valuable elsewhere. Among the .35s, the one with no means of attaching mufflers is the best, the one with a post in the center of the exhaust is next best, and the one with ears on the side of the exhaust is useless. Other G.21 displacements were .29, .40, and .46. Stunt people like the .46 and might give lots of bucks for one.
If it's a new .35, let's talk.