You might be able to convert to rear wheel disk brakes from a Camaro. The rear ends are similar(both are GM 10 bolts), but do have some differences. It might be easier to check aftermarket companies for a conversion kit.
There is a kit for the G-bodies(monte carlo,cutlass,regal) that might work for the front. I know the 1st gen S-10's use the same spindle as the G-body cars. If you just want better braking, try updating your stock brakes. I would use slotted rotors and some good metalic pads. Avoid the cross-drilled rotors. They are prone to cracking, especially on daily driven vehicles, plus they are really expensive. You could also get metalic shoes for the rear drum brakes. Why do you want bigger brakes? Do you race the truck at all? Good luck and let me know what you find out. I have an 85 S-10 X-cab that could use better brakes-- especially when towing(or racing!!). Later