I didn't get a pic of the smaller cavity but here is the larger cavity. I just needed a small amount of additional room. It's not the best constructed body but it sounds a thousand times better with new components.

quote:

Originally posted by Rustyblade:
Dermal has a sander bit. A wider drum in the shank. Perhaps that extra 1/4 inch width on the inside chamber will suffice.

Seeing the picture, the dermal will work but be dusty/messy.
I'd nibble away with a 1/4" chisel and exacto knives

Dremel makes a flexible shaft to which bits are added. A hogging bit on the end and you might be able to excavate enough material, it will take time.