Can't cut tbe floor. You ever see the bottom of a 65 Chrysler? Doesn't look anything like the Challenger. Would love to use the 518 if it would fit ok. Looking for the simplest way to overdrive the car without selling a kidney. I considered the gear vendor unit when I built the challenger but decided against it. Why add weight with an old tranny when you can just use a newer style trans without the added weight. Besides, I already have a 700r4 sitting on a shelf in the back of the shop.