The 90R3 is not enough engine for this kit. The largest 4 stroke engine suggested is a 1.20, and the 170R3 will put out just about that amount of power. That is a lot of engine to have on such a long nose though. But, the 90R3 won't have enough power. Cutting some cooling openings in the cowl wouldn't be a bad idea for your radials, and would make life easier when tinkering around it at the field.