4spd swap checklist for a 68 Dart GT 318/904
there was a 8 and 3/4 sure grip center recently listed here for I believe $900.00. It was a good gear 391 if I remember right. 355 is my favorite but depending on what your looking for maybe it would work for you. I did the Coronet R'T in 1982. but I had a complete donor car and we made the 440 body into an R/T. I sold it years later after doing an old school lacquer mopar "electric blue" paint job with white vinyl top. Dude did some tach wiring to it and it burnt to the ground along with his garage and it caved in on top of the car. I should have never sold it to him.