my '58 chevy parts book says that the 3600 (3/4 ton) pickup did have "open" drive from '46 thru '58 (probably later on too) with a 4.57 ratio. The book would not give me a lug count only the 1/2 ton had the torque tube! the center section casting number would be 3699535
Ken's right a 67-72 gm auto V8 truck will have 4.10 & the center section will bolt right in. I did this swap in my '50 1 ton & love it! My 261 likes it on the highway too!
I bought the truck last week. I am not sure what gears are in the rear end but the PO said it would pull stumps out of the ground (AKA low gears?)I though he said it has 4.11 gears. So i need something that will be better on the highway. So do I need high gear? 3.55 maybe? The 76-72 GM V8 swap sounds like the same gears I already have in the truck.
with tall tires, you should be fine running 55 on the highway. I ran up to 65 with mine with the stock 4.11 gears and stock tranny.
The next step is to put in an OD tranny - you will not find a better ratio (numerically lower ratio) for that housing unless you find the very rare 3.90 which is hardly worth the effort if you already have a 4.11.
I have an A833 tranny which gives me a 0.73 OD for 4th gear - would make 70 mph a dream at about 2500 rpm with your setup.