You didn't respond to this posting so I went back and looked at your previous post (Cpp six lug disc brake conversion).
You are now aware that original 15" wheels don't fit your disc brakes. You were given advice (other options) but you didn't respond to that posting as well.

People normally have the same size tire for front and rear axles so they don't have to carry two spare tires. Tire height, rear axle ratio and final gear ratio of the transmission affect your top speed (highway). Changing rear tires can affect your speedometer. Looks like you decided to stay with a torque tube drivetrain.

What size tire were you planning to run on the rear axle?

"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."