Look at the SPID decal in the glovebox. A regular-cab truck likely has JN3 brakes--the weakest power brakes ever put on a GMT400. That's what my '88 K1500 had. They were so pathetic that GM quit using them in the early-'90s.
The difference between JN3 and JN5 is:
Rotors (thicker, but same diameter. The thicker rotors need the matching hub/bearing assemblies. I just used the entire steering knuckles from the donor vehicle.)
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Calipers (larger piston, but "low drag" design like the JN3. The pads are essentially the same except the JN5 has a bigger spring-clip on the inboard pad to fit inside the larger piston. I think I just stretched the spring clip on my pads since they were still usable.)
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Master Cylinder (1 1/8" main bore, 40mm Quick Take-Up bore. JN3 is 1", and 32 or 36mm QTU, I forget which.)
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Brake booster (larger)
(Photo coming...someday.)
The RWAL and rear brakes are the same. The rear brakes SUCK.
If there are differences in the combination valve, I don't know about 'em.
The front brakes, master and booster can come off of an extended-cab K1500 or a light-duty K2500. A newer regular-cab truck should also have JN/JB5 brakes.
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My '88 had no front sway-bar. I stole one off the same extended-cab donor vehicle that supplied the front brakes. Very worthwhile. 2WD is different from 4WD. Be sure to get the correct one.