D-LOCO;
You didn't mention the location of your battery & servos - if you can move these forward it will help your balance and weight problem.

As to the engine; If it is possible I'd move it forward too. The cowl can be recut to fit the muffler & mix control, if you are concerned about the existing holes -they can be patched.

A key factor to a good plane is to keep the weight DOWN! [:@]

Good Luck!