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go to the YouTube link above to see Stacy David's TV Show "Trucks" in which he builds a "67-72 Chevy called Copperhead. and he gives you everything you'll need to know about building one of these models includeing answering the heater/AC question you originally asked.
as for value, ALL of these vintage chevy trucks are going up in price (if not value) on a daily basis now.. and once modified, the value becomes whatever your willing to give for it.
but when considering that a new truck STARTs at around $35,000.00 and knowing that even if you put another 10K into an older model for a frame off resto, and do all the work yourself. its not out of the question to toss 10K on a good running, decent looking truck. but as always, let the buyer beware, and to each his own.