I replaced the rear in my ‘55 373 with a D-80 which has disc brakes to match front disc brakes I put on there. 5.13 ratio in it which I will change. Also have a Brownie in there. My bolt pattern is 5/10 on 7.25” so important to get same. You probably have same bolt pattern, so have to find that first. Those and similar rears come in two widths, about 7’ and about 8’ wide, depending on body style.

If you have a different bolt pattern, then D-70, GM ff 14 bolt would work. Then one has to get modern wheels and tires unless one wants to keep 20’s. 19.5’s are the only commonly available modern alternatives. Unfortunately they look undernourished compared to 20’s.

Some motor homes came with these axle/wheel combinations, need solid axle variety. Otherwise look in wrecking yards, dead roadside vehicles, tire shops for 19.5 wheels.

Good luck,

Ed

'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.