I kinda have to laugh at all this as back in 1974-75 the winged warriors were all worried that gas prices would kill the wing cars and could we put a 318 in and keep the cars value. I mean gas is the cheapest part of any car ownership. To the OP buy the rarest engine and trans combo you can afford. If you really want to drive the hell out of it a tanks inc fuel tank, fuel tech injection, and good electronic timing control sets you back 3 grand and can mostly be hidden under the air cleaner. A superbird that is driven can in no way possibly compete with a freshly restored panel fit fresh paint, nut and bolt show quality bird, but that is a good thing as the mods take nothing away and add enjoyment. I think you will find a bird is a pain in the ass these days the way people drive, videoing you going down the road☺, but I hope it all works out for you, do not be afraid to mod the car, always buy the rarest you can afford.