Doc,
The 1937 1/2 ton truck used the Delco 948R 3rd brush generator.
Many of the pre-1940 trucks have been upgraded to incorporate a two-brush generator with a firewall-mounted voltage regulator. If your truck has a voltage regulator on the firewall, then you'll want to acquire a 1940 or later generator.
If you go to a later model generator, you may need a different mounting bracket, as I believe the later model generators were longer than the 948R. I'm not sure, but I think the bolt holes in the block where the generator bracket mounts are the same for all the 216 motors, so a longer generator bracket should bolt right on. You'd want to make sure the generator pulley lines up properly with the crankshaft and water pump pulleys.
I just bought a used 948R on Ebay for use as a spare for my 37 1/2 ton, but haven't received it yet. If it rebuilds and road-tests OK, I'd be willing to sell you the spare generator that I have now. It is an older replacement generator, the same size and type as the 948R, though I don't believe it is a Delco, as there is no tag on it, and I don't see rivet holes where the Delco tag would have been. I've put several hundred miles on this generator and it works fine.
Use the search function on this chat site and search "948R". You'll find several threads on the 948R generator. The thread on the 1938 headlight switch has some useful info.
Mark
