The 4.10 center section that was used behind automatic transmissions is a direct swap into the Chevy corporate housing. Those gears are not being produced new by anyone, and OEM is extremely scarce and pricey. The usual ratio for a stick shift C20 is a 4.56. There's a Dana type 60 8 lug rear that was used by GMC that's also pretty scarce, but there are all sorts of aftermarket ratios available for that one. I've got one of them under a 59 Suburban with a 3.73 gearset for a Ford, in a GMC housing.
Jerry
