I put P3500 HD axles under my '37 GMC, but was able to move the front fenders out 2" with spacer blocks, works well without no tire stickout. Unfortunately, that is not an option on your AD. Some good body persons have added a strip of 'tin' in the appropriate place to widen front fenders.

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.