LT,

Have you check the diameters for other 15" tires? You might be able to find a 31-32" diameter 15" tire.

I do not have an answer about backspacing (wheel offset ?) or maximum diameter; but, on earlier 1/2 and 3/4 ton trucks, the offset ranged from 0" to 9/16" and the loaded tire diameters ranged from around 28" (15" and 16" inch rims) to around 31" (17" rims on the 3/4 ton).

My guess is that the diameter will be no problem but the 4" backspacing/offset might be a problem

Maybe someone with first-hand experience will respond.

Tim