I am rebuilding a 1973 f250 4x4 (highboy) its a retired fire/rescue truck, it has dual rear wheels (I know that it is not stock) and a fiberglass utility body on it. The front tires a 235/75/16 and the rear tires are 216/75/16,, was this a common thing to do from the factory, or should they be the same size all the way around.

 

Same size all the way around. They may have beefed the fronts a little but were unable to use that size in back due to wheel spacing--maybe. There shouldn't be enough height difference there to cause trouble in 4 wheel drive. What rear axle did they use? Check your ratios front and rear.

 

The rear is a D60 4:10 and the front is a D44 not sure of the ratio