looking for some input

What do you think a 1975 Dart sport, /6, a/c, 7 1/4 rear, is worth. Other than a couple of small dents in the drivers fender the car is EXTREMELY clean and original. There is absolutely no rust at all as it has been garaged its entire life. The guy said he wants $3000 but I think I could get him to $2500. The car is all original light green paint and interior. I would be putting a 340 and 904 into it. What do you think it is worth.