Very cool!
Hope you get it fixed.
There was a 1960's Chevy C50 dumptruck at the junkyard here that had one of those over/underdrive units. The tag said Dana/Spicer on it and it was mated to a SM420 4 speed. It had Under, Neutral, Over, and Direct, I think that's what it looked like on the shift knob. I knew I should have asked how much he wanted for it but the truck got crushed before I even remembered to ask about it. It sucks 'cause that truck just needed some carb and brake work and it could've been a good truck.