Does the blower motor run? Can you hear it? If it doesn't, check fuses....all of them..... as some my be control power for relays. If the motor runs, then you may have a failed vacuum switch (it is positioned by the function lever on the HVAC panel) or a bad vacuum motor or two. The flapper valves controlling how and what kind (hot/cold) of air is routed through the HVAC plenums are operated by vacuum motors. If they are bad (leaky) they won't open/close the valves. You may have leaking vacuum lines from the engine. If it's an '87 and still has the original vacuum hoses, that would be a good project to attack.
High pitched whine.... from the engine or transmission? Check all the vacuum and emissions hoses for leaks/cracks.
Body, frame, engine and resto parts: LMC Truck (
www.lmctruck.com). Go to the website and sign up for their S10 cataolg. I've ordered from these folks and they are good people.
Hope this helps,
Mike