Tried out some different things with a mechanic friend today and got the speedometer to work. We kept checking each part of the puzzle, and found that the angle on the impulse generator was causing the problems with the speedometer not working. Connecting the generator directly to the output of the gear on the transmission resulted in the speedo working, but showing too low a speed. Inspecting the angle, it doesn’t appear to offer any change to the rotational speed hitting the generator module, leading us to suspect a problem with the generator itself.
So now I need to find a replacement generator and angle and see of everything works after swapping in a new unit.