3.42 gears. Very common on 1500s. That's what my '88 K1500 has.
AAAAHHHH!! The worst, weakest power-brakes installed on GMT400 trucks.
You absolutely need to deal with this before suspension upgrades. (Suspension REPAIRS are another story.)
The nearest Treasure Yard that has a C1500 extended-cab, or a C1500 regular
or extended cab newer than...'92, perhaps. Kinda guessing that a C2500 light-duty (6-lug) would be the same up-front, master, and booster. Check the SPID sticker in the donor's glove-box, look for JB5 or JB6.
You will need the rotors, calipers, master cylinder, and power booster. I have not converted a 2WD, I'm assuming that the wheel bearings and steering knuckle are the same on the C-trucks. The front bearings/hubs are NOT the same on the K-trucks. Maybe you wanna grab the steering knuckles from the donor truck, just to be sure.
Having converted the front from JB3 to JB5, you still need to deal with the rear. You have the 254mm (10") leading-trailing shoe drum brakes. What you want is on the upgraded axle, 11.x" Duo-Servo rear drums. Bigger, stronger, heavier; and not as sensitive to park-brake non-use as the leading/trailing design. Upgrading the front and the rear gives you the equivalent of JB6 brakes.
The "Kit" to replace my JN3 front brakes (plus a master cylinder and booster, not shown in this photo):
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K-series rotor difference: "3" rotor is narrower than "5" rotor. Diameter is the same.
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The caliper pistons are also larger on the "5" than the "3", which requires a bigger-diameter master cylinder, and a more-powerful booster. MAYBE you turn-in the Treasure Yard parts as "cores" for "rebuilt" parts...but be sure to take the Treasure Yard parts even if you don't plan to use 'em. I pulled the calipers and master cylinder apart, cleaned-out the sludge, dreck, garf and garfelderfarb, put 'em back together and they're in use on my K1500. I used the old disc pads (nearly worn-out) to clean the rust off of the rotors for about a week of use, then put new pads in the calipers.
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For ****'s sake, do not install an "NBS" GMT800 master cylinder on low-drag calipers (JB3, 5, 6)
There are aftermarket brake upgrades (be careful!) and there are upgrades from newer-generation pickups that I'm not really familiar with. What I've posted is cheap, available, OEM-verified, and effective.
Flush the brake fluid while you're in there. If you have an iron-body RWAL unit, it has a bleeder screw. If you have the newer aluminum-body RWAL, you'll need a scan tool to bleed it properly.