Looks like you have the optional dually rims and springs.
Looks like front and rear are 8 bolts on a 6-1/2" circle (previous picture).

I'm a novice on the big bolts but I see want ads for brake drums like they are hard to get.
Before you focus on rims and tires you may want to first look at brakes and your type of rear axle before you work yourself corner.


"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."