What do I offer for this engine?

I am sort of looking for a big block to stick in my 72 Chevelle. (Isn't everyone?) A friend of mine called last night and knows a guy who just bought out another guys pole barn and back lot. I guess he got several older pickup trucks, several small block engines, a lot of junk etc. When they were looking around, inthebed of one of the trucks under a topper is a complete 454. He doesn't know what year or what it came out of but my buddy told me he would be interested in selling it but does not know what it is worth. He told me to figure up how much I would give for it and let him know. Now I know I would have to go see it to see what kind of shape it is but what would you think a ball park offer would be to start out? Also what years would I not want and how would I tell what year it is? I am not in a hurry right now for an engine but if it was a good deal I would get real interested.:yes:

Thanks for any replies.:beers: