Looking for a proper filler for a relatively large hole

Hello, I'm currently working on a 1982 dean that somebody cut a pocket into (the hole dose not completely extrude through the body) for a whammy bar. I want to fill it in but don't know what wpuld be a good filler. I have machinined a block to fit into the pocket and am also wandering if this is in any way a good option. The block is made out of G2 it's a very dense fiberous composite material( about the hardness of mahogany maybe harder). The hole is 1.034 deep 2.5 wide 2.25 height. If you could tell me a good filler for a hole of this size you'd save me lots of headache. Thanks for your time