I presume you have 5/10 on 7.25” wheel bolt pattern. Your two ton front axle will work fine, a replacement rear axle with that bolt pattern and disc brakes will work on your truck. Dana-80 axles have several suitable ratios. Look for modern heavy pickups and C and C Chevy/GMC trucks. 19.5” wheels and tires are almost the same OD as your original 20” tires. Disc brake front hubs/spindles can be added to your axle. Some fab. skills required.

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.