I believe you guys are right, 1960 was the first year of the 1/2T 4x4s and they were built by GM with Dana 44 axles. All previous were 3/4T Napco's. My '62 has a Timken 4 shaft transfercase, same thing was used in Duce-and-a-half's, it has provisions for a PTO to the rear and a second rear axle. Rockwell might be the same thing as Timken, I don't know about that. The transfercase was used with small mods for quite a few years after that, perhaps to 1970 or so. Eventually it was mated directly to the transmission. Mine is divorced, I am sure that is a holdover from the Napco "kits", no engineering required as with a mated case. I believe but have no data that the larger trucks used the very same setup with rear axle assemblies cut and knuckles added by Napco for the front and the same transfer case.
The hubs you posted the link for are for something smaller (1 ton), the Summit link said Dana 60 & 70 external hubs, 3 9/16" bolt circle. I measured a spare drive flange that came with my C50 and it's 8-bolt circle is 5", and the spline count is 16, and axle diameter to bottom of spline is 1 9/16" (or thereabouts). I am going to have to scour the USA to find locking hubs! Any input/leads as to who might have them (old wrecking yards that deal in 2 ton trucks, etc.) would be appreciated.
Also, the NAPCO 4WD units were line-installed in GM 1/2 & 3/4T trucks from late 1957-59, using a Dana 23 transfer case. Ford used a mirror image of the Dana 23, it was named Dana 24, and was used into the 1970s, before going to the NP203 or NP205 cases. The 1960-69 Transfer cases used in GM 1/2 and 3/4T is the Rockwell/Timken T221 like you mention. In 1967 GM married it to the manual trans, either 3 or 4 speed. Discontinued after 1969, and was never married to an auto trans. The NAPCO front ends for 1/2 & 3/4T were discontinued after 1959, replaced by the Dana 44 for 1/2 & 3/4T from 1960 on until 1977-80. The NAPCO front ends used the same drop-out 3rd member/differential as the rear end of the truck, whether 1/2 or 3/4T. One note on the Dana 23 transfer, it was not used in 1955, beginning in use in 1956. 1955 and older NAPCO conversion transfer cases were different (I'm not sure what brand, would guess Rockwell/Timken) in that the front output was on the driver's side (like a Ford transfer). Also, the front end on a 1/2T was 8 lug! The rear end was the standard GM 1/2T rear, but with wheel adapters to convert to 8 lug! I know this due to having parted out a 1955 Suburban 4x4 that had this setup in it. I believe the same set up was used in pre-1955 4WD conversions, but am not privy to those, as I only concerned myself with the 1955-1959 NAPCOs in my 30 years of toying with these things!
Regarding transfer case for trucks bigger than 1 ton. The Rockwell/Timken T223 was used, and looks like a 50% bigger T221. I included a picture of one here. I have a Ford version of a T223 (taken from a 1959 F600 with Marmon Herrington 4WD conversion) and it is the same as GM used except the front output is on the driver's side. In my C50, it does not have a T223, and I am trying to figure out what it is (need to crawl under it and look for numbers). It may be a T226 case.
Oh well, I love researching these odd-ball 4WD trucks! I thought the NAPCO was hard to find info on! NOPE! These bigger (over 1 ton) trucks are MUCH harder to find info on!
