I guess I thought the balance issue could be resolved with proper placement of components. I now realize that may be wishful thinking. The engine length issue is something different. The Saito 120 is 138 (5.44 in) mm long. I looked at the plans again, and realize I will have to move the fire wall 3/4 to 1 inch aft. This wall also impact other nose area structure including the sides, bottom, and other formers. The Saito 100 is 115 mm long and will fit in perfectly.

The thing is, everyone I've ever talked to says a 120 4C is perfect for this airplane.

AAARRRRG!