I have one of the blue Dymond Bearcats. I dont fly it anymore do to its a little beat up and not looking good.
I had a .61FX with a pitts muffler in it and it was just the right amount of power for it.
I would not go with a .91 2 stroke, it would be a little too much for this plane.
Yes, make sure you reinforce the stab. real good(poss. sheet it) be fore you recover it. Me and other Dymond Bearcat owners had big problems with futtering and breaking. Also try to reinforce the area inside the fuse where the stab. goes threw(add more wood for supporting the stab.).
I would NOT cut this wing down anymore, its only 53",and i wish it was like 56", it needs it.
I like this little Bearcat, it flys great and looks good. You dont see many Bearcats out there.
The only things I hate about it was, the stab problems and the wing stall(plane stalls fast at slow speeds).
Enjoy!!