Robert,
You may want to mount the engine back about 3/8 inch if you can and not hit the carb. Cowl will go back that much and mount better. Saito 72 and OS 46 FX or 50 SX weight about the same. Surprised that you are having to move weight that far back.
Helped with one the other day that has a Saito 65 (brick) in the nose and the battery did have to go behind the servo's to balance. Sure you are measuring the cg in the right place.

The landing gear looks light, but he plane lands lighter.

Ed M.