[Bill Hanlon]

Both those rear ends look like Spicer 45s to me. Both trucks should have come that way. The 58/59 "power lock" differential was still based on the Spicer 45 and was available both in 3.07 and 3.92:1 ratios. From the outside I don't think you can tell the difference between the "power lock" and the standard Spicer 45

My Master Parts Book lists a bunch of "power lock" specific parts, but has no drawings of them.

Nice find of the tach on the '57. The real tach from GMC used the same mechanism, but with lettering that matched the rest of the instruments. There are people around who will redo the guts in the tach to make it work without needed the sending unit which were notoriously flakey and needed a 1.35volt mercury battery.

By the way, I have a .PDF file of the '54 Hydra-Matic shop manual if you'd like it instead of buying the '57 manual I pointed out on eBay the other day. It is probably 99% the same. Only real differences are the larger torus unit on the V8 engine and different shift points because of governor and throttle body tweaks. If you want it send me an eMail address and I'll forward it to you. Total size around 21 MBytes.