you can tap off the ground pin on the NESmod pcb if you wanted.
If i remember correctly i made the unused plain on the bottom of the PCB a ground plain.. so anything u see a lot of parts connecting to the same HUGE ground pin should work. but i'd just solder it to the ground pin on the power connector... Pin 1.. Black wire connects to it.fit it anywhere you can find a place. I put it next to the NESmod pcb. but i also drilled all 3 holes out at the same time so i knew they'd fit.
Muchos danke! Once I get everything in order, I'll see what will work best.