Craig - His 3600, unless changed from stock, has the 8 lug 3/4 ton rear axle.

Rob - I think you are more likely to be looking towards an axle upgrade like in this Legacy Tech Tip, AD 3/4 - 1 Ton rear axle Upgrade.

Or maybe an alternative later 14 Bolt Axle Swap as written up by fellow Bolter Grigg.

Of the two choices here, the later by Grigg may be easier to find parts (newer trucks) as the HO52/HO72 axles with 4.11 ratios in the earlier trucks are getting pretty hard to find these days.

I'd suggest giving both of these a good read, then come back and ask more questions depending on which direction you decide to go in. wink

~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)