A body off resto refers to a full frame type car,your Challenger is a uni-body type.All year Challengers and Barracudas are worth good money restored but you are correct in that a `70-71 will always be worth more.Of course finding a nice `70-71 model will cost more so you need to consider how much $ you have into yours and what shape it`s in.Also consider that if you drive it often that will quickly devalue the car due to wear on the undercarriage,if you want a driver I wouldn`t go too crazy detailing everything to show quality.