i really don't think i'll need to cut the top tube or modify the tank at all.
I'll have to modify the lower mounts, but i think i can cut/rotate and make the cradle area slightly larger and I can pitch the motor slightly to the front if I need to. The CRF150 motors fit easily, and this 200cc lifan is just a tiny bit taller.
I'll be able to do a test mock-up soon, motor is on the way and the chasis is in my garage.