Thunderbolt,

The engine you have there is a RCGF 65cc. It's a bit of an antique but makes very good power and is extremely reliable.
One thing to check out for is hub run-out, the early models had problems here.
It will run props in the 22X10 to 28x10 range and do so until the fuel runs out. Enjoy it, I have 2 of them and I am always amassed how well they run.

Regards
Andreas