My brother in law is in the auto salvage biz. And to be honest, he has been doing it for some 30 plus years, he don't have a clue as to what things are worth in our line of things. I do know, if you call him for a price on something, say a engine for a whatever, he can usually tell you how many miles is on it, and most often is cheaper than other yards.
But Dough unless your "friend" has a large enclosed building, it's makes more sense to leave it on until called for. I know my BNL has had so much stuff ripped off over the years it's pathetic. HE has bus's, Vans, building, Box trucks and so on with parts such as PS pumps, AC pumps, and so on.
I have sent several folks his way looking for this and that, always a positive feedback. Unless you walk in or call acting like an A$$.
Like most yard owners they collect and collect, and as one gets scrapped out, the crusher comes in. I know at one time, he had over 500 67, 8 and 9 Cameros. If he could have sit on it for another 20 years, he would be sitting pretty now for sure.
So much there that will bring quick cash for metal. Aluminum wheels, heads, and tyrany's. Then there are the CAT's, and the list goes on.
So being a good question, it's almost impossible to answer in a few paragraphs.