The fan unit in the F-86 is 90mm and overall height from top to bottom inside where engine mounts is 121.67mm/4.79". If you divide that number in half I have almost 61 mm from engine beam to fuse top clearance, but you'll have to subtract about 5mm for head clearence. so if I replace the fan unit with another system it can't have a radius of more than 55mm from the center of the crank on motor. maybe I can sqeeze a hot .21 on a 720 kress fan in the fusealage, I'll have to go to the hobby shop and check out the motor heights, including that I hack off 2/3 the buggy cylinder fins. It shouldn't over heat with the air flow of the fan unit.[:-]