I Have an os 70 ultimate in mine plenty of power.
no cutting of the cowl needed exept for the cooling holes.
But i am having trouble keeping it cool these 70 ultimates need cooling arrond the crank case to stop the pump from vaporising i think i need to work on some baffeling from the oposite air inlet to force air arround the regulator at the back of the crank.
I think the air is going arround the motor in the cowl not cooling the motor.
will come up with something in the next few weeks.