This is the best compromise-pot I could find. It can be mounted on the PCB with mounting brackets and the power rating and size is ok. Resistance range maximum is only 1M (Prodigy uses one 2.5M and 5M pot) and audio-taper (log) maximum is 500k (Prodigy uses four 1M log pots). This is a high quality conductive plastic pot that should last forever. I must check the technique where you can approximate a logarithmic law by resistive loading a linear pot. I assume you can also change the value of the pot with some serial resistance.
Smaller board-2 is now traced and cross-checked. I created the Bourns PC pot part-layout to Sprint Layout. In the picture below I match the pots to this PCB-layout. I have also ordered the DP3T and DPDT switches from UralTone (Finland) and Banzai Music (Germany).