I say chalk test. Pressure will vary from vehicle to vehicle. If you asked the manufacturer theyd want vehicle weight along with all the mods that may make them heavier.
Get sidewalk chalk, color a good portion of the tread(nothing crazy just a couple inch wide astripe across), Drive in straight line on fairly flat surface 50ft (get quite a few good rotations out of the tire).
If the center wears it means less air, if the outside edges both wear it needs more.
Take the air up or down ~2-3psi each run. When chalk wears off the tire evenly across the whole tire you've found the optimal setting for your rig.
I run ~28psi front/~25 rear
84 xj 350tbi, sm465, 203/205, 60/70. links and other junk.
what size sawzall blades does it take to fit 40's?