I don't know if it helps but I find that mostly the PCBs follow a standard layout grid, where the top row of pots is generally 25mm (1" I guess) from the second row, and the distance between the pots from side to side with two pots is around 41mm, which I guess would be around 1 5/8". Sometimes there is a third knob in between, so half-way between 1 5/8". You'll probably want to check the side to side measurement - I don't have a PCB handy.