The instruction manual for my 4*60 ARF doesn't include any informtion on how far from the firewall the engine should be located. I was expecting some reference to distance between firewall and thrust washer. That's the way the instructions for my Alpha worked. Obviously the thrust washer has to be forward of the front edge of the cheek pieces on either side of the engine, but I've go no guidance and at least a half inch of play room. I'd rather not have to add weight at either end to compensate.

Is there an optimum distance from firewall to thrust washer to minimize CG issues after I've gotten it all assembled, or should I just make sure that I've got reasonable clearance between the prop and the front edge of the cheeks?

All reports say the 4*60 ARF tends to assemble tail heavy, and that was the case with mine. We put the battery pack under the tank, against the firewall. Then we slid the engine fore and aft on the mount until we got it balanced. I can't really get to the plane right now to measure anything.

It sounds like I should do the same, then. Finish assembly and then determine final location for the engine and battery to facilitate using as little dead weight as necessary to achieve proper CG