Hello Jim,
For the Stereomour, did you get the four pole three throw or the three pole four throw? (Either would work, but the four throw will have an extra position, maybe you could drill and mount a 1/8" mini jack on the front of the chassis?)
Assuming it is the four pole three throw, you will want to start by orienting the switch so that one of the two flat edges is facing you. Starting at the top, you can feel one of the mounting screws that holds the PCB to the switch itself, working clockwise from there, you have input 3, input 2, input 1, and common.
This pattern of four repeats itself around the switch, with two complete sets on each half of the PCB.
The three pole four throw switch is a bit more difficult to describe due to symmetry issues. I will be mulling over how to describe this switch just in case.
-PB