Agreed with DH.

25% or so on the CG. This point (CG) is not negotiable regardless if the radio gear weighs 5lbs or 5oz.

Modifying the airplane to shift the wing rearward would probably work, but isn't that a lot of effort now that the airplane is built, and everything is shaped?

Models of the type you describe just weren't terribly large, so I'm puzzled by the need for "pounds" of weight in the nose to balance, unless something went horribly wrong in the construction somewhere. OSB ply instead of balsa in the tail perhaps?

Liquid nails, and copper flashing for the tail fillets will do it everytime.....<GG>

Stick to the plans, and there's a good chance the model will live to fly twice.

Good Luck!