Mods:
If you want to add a volume control, start with a 100k pot (other values may work better, that's just what I'd try first), connect lug 3 to the Out pad on the board, lug 2 becomes Out, and ground lug 1. It may also be useful to add a pre-gain pot at input. Again start with a 100k pot, lug 3 becomes the new In, lug 2 goes to In pad on the board, and connect lug 1 to ground via a low value resistors (470Ω, 1k, etc). No idea how useful these mods would be, just a few basic things that came to mind as I laid it out. If you're adding a Volume control, it might not be a bad idea to put a booster (LPB-1 would work well) between Tone 2 and Volume 3. YMMV

