I am attempting to put the 77 radial engine on a top flight corsair ARF. there is only about 3 eighths of an inch clearance all the way around to the heads on the motor and the inside surface of the cowl. but the finished weight of the model is about 22 to 25 pounds, which is a great fit for the 77 radial. I have a back out plan to slightly enlarged the cowl if I need to.