A 261 engine would bolt right in, would help some. Look for tubeless(22.5) rims, work on P-30 front spindles, two speeds are almost all low and lower ratios, so don't waste your time there. A Brownie would really help, hard to find, though. A 292 would help even more, but about 3" longer than 235/261, but doable. NV-4500 OD trans would help if can pull it.

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.