Thinking about buying a 1982 dodge challenger?

Well the car itself looks like a good idea. I mean the car has only 82,000 miles on the body and the was just rebuilt. The interior was just redone and it looks sharp. The only thing is, is that the engine was replaced from a 4 cyl, to a recently rebuilt 5.2 liter v8 that came out of 1989 ramcharger. So here are my main concerns. The airconditioner was taken out so is there a possibility of putting one back in? And a ramcharger gets like 11 to 16 mpg so could expect somthing better(if i dont drive like a maniac)? The car runs strong and they want 3500 for it. Is it a good deal?