If you want to go the Mopar route, there are a few cars that are pretty easy to find and that are relatively cheap. I'm just going to go ahead and leave the expensive years and models out.
1970-75 Plymouth Duster- prolly the cheapest and easiest to find out there, obviously earlier years are preferred (ram air hood, 340, go wing, shark tooth grill, etc.)
1968-69/73-75 Plymouth Roadrunner- Easy to find, later model RR were used as police cars.
1970-75 Dodge Dart- pretty much the same car as the Duster, just the Dodge model.
1973-74 Dodge Charger- I really like these and seen alot of these go pretty cheap. I actually passed up a trade on one for my older truck, and i'm still kicking myself for not going through with it.
Those are the main ones, but i'm assuming youd rather want a GM car so you can find a home for the 327.