The import pickups are going to be the only ones I know of that have an axle that is narrow enough to fit under the fenders properly. They typically will be either 4.10 or 4.88 gear and 6 bolt pattern. Find that first and then match the t case to which side the drive shaft is on the axle.

If you are wanting to keep it GM, you will have to start with a S10 which I think would not be ideal for your app. Another option that is not as bad as most think is to have the dana 44 or 8.5 10 bolt cut down to proper width. Narrowing a housing is not hard and then you order custom axle shafts from Moser or Currie etc. They are not very much more than new replacements if you don't get the biggest and strongest ones but they will be stronger than the stock axle shafts which is not a bad thing. This will get you disc brakes and open knuckle steering and very common parts like bearings, seals, rotors, pads calipers etc. You can also get any ratio for them to match whatever rear you want.

1937 GMC T16 468 BBC th350, 4.10
1941 Dodge COE 5.9 cummins, 9 speed roadranger
1947 Diamond T COE, hercules and 4 spd, all original
1955 Chevy LCF 9.0L IH diesel AT545
1962 Corvair (Elsie)
1967 Jeepster Commando
1968 K10
1970 Chevy C50 box truck