There's a lot of material you can cut away on the K&B. Take out all the exhaust above the aeration plate and cut pretty close to the screws on the lower unit up to the engine mount.

You will need to make a motor mount to connect your motor up with flex. You can do this by cutting in to the lower unit deep enough for a coupler or you can just raise your mount high enough to fit a coupler in between the lower and motor.

Either way, I'd recommend getting a new motor. At least a brushed 700 size can.

Ryan