I don't know what your plans are, but getting different tires is frequently one of the last choices; if they I'll hold some air, it might be worthwhile to do many other things.

Rear diff. ratio?
New rear axle?
Different braking system?
Wiring system?
Hydraulic brake system?
Bed wood?
Tin-nice name on the doors?
Grille?
Different wheels?

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.