I got this engine from a friend and want to know its characteristics and what prop should I use for a Daddy Rabbit. Is this the .61 or .65?
I believe Morris Hobbies used to sell this engine.

I think its the 65.

The 61 had a black head I believe. Good budd Gary Kirby used the non-pumped 61 way back in early 90's in Jax. Turned a 12x12 apc with authority on a slightly stretched pipe, 20% nitro and KB1L plugs

The 65 should turn a 13x10-11 or a 14x9. Set the high point of the pipe at approximately 15" from the exhaust flange, straight line.
MattK

What kind of rpm should I expect with these props?

should turn 10 to 12 thousand maybe more