<<...YS 63...still nose heavy...>>

So was mine. Even with the battery under the servos, it still wouldn't snap well.

Keep in mind that the YS 63 is considerably smaller than the Saito; about the size of an OS 46 FX, in fact. If it is not too late, you might want to move the firewall back a half inch or so to allow for carburetor clearance on the Saito.

In any event, make it a four-stroke. My first SE had a .46 two stroke, and while it was plenty of power, the torque and larger prop of the four stroke makes for more pleasing flight characteristics, IMO. You can FLY through manuevers, as opposed to darting through them.

YMMV...

Steve