It looks like a nice engine to convert; somewhat like an Echo actually. I don't make a backplate mount for engines like these. I just put studs in the four crankcase holes, and mount the engine directly to the firewall. Sometimes it is a bit of a pain to get to the nuts inside the fuselage behind the firewall, but it does save some weight and the hassle of making a mounting plate with counterbored screws mounting the plate to the engine.

AV8TOR