Outlaw66

hello ford brethren. i want to consult you guys for a little problem of mine. im getting ready to buy a 5.0 from a guy and just wanted your opinion. It will be coming from a mid-late 80's big car, probably a crown vic or a mercury, and will come with an AOD. I'm planning to swap it into my 66 mustang coupe. I haven't seen the engine yet, and i was just wondering what year would be best? I'll be switching it over to a carb, so i'm not concerned about fuel injection or smog. How do I tell if it has a roller cam? Are all 5.0's roller? How much should I pay? He has a bunch of em, and I get my pick. i've never dealt with a 5.0 before, and I figured you guys new a lot more about it than me. thanks in advance.