1988 k1500

There is a pin in the trans that is broke, There may be someone more knowlegeable that can explain replacement.

If you have drum brakes, you may be able to remove the rear drums and adjust the shoes out enough so that there is slight drag. Assuming the brake cables are moving.

There are adjusters in the rear drums that you can adjust to keep your parking brake tight. Go under the car and remove the plastic hole covers and use a brake adjusting tool to tighten the brakes. When you have just a slight drag on the brakes then they are tight enuff. This should keep your parking brake tight. This adjustment is supposed to be automatic, but they will freeze up and not adjust.
If after you tighten your brakes, and your cable is still loose, then there should be an attachment adjustment somewhere on the cable. They are usually at the level in the car, but I have seen them in the middle of the cable under the car.
I would not remove a tranny for your park lock being broken. Make sure you set the brakes and drive it til something major breaks in the tranny.