What are your plans with the car? Are you going the modified route or are you wanting to keep it as stock as possible? The reason I ask is that 73-74 Challengers used a special material for the headliner. It's NOT the standard perforated material that the 70-72's used. Many places sell the perforated style and it is pretty cheap. It will fit your 74 just fine...it just won't be stock.
If you want the stock look, you'll need to buy a headliner made with Yorkshire material. It sort of resembles corduroy. They are about twice what a perforated headliner costs. I got mine from Dante's Parts. He can get both styles and was good to deal with.