I'm running the stock 318 and I presume 904 Torqueflite auto in my '73 Duster. It has a 7 1/4 rearend. I'm really wanting to put a 8 3/4 in it with a Suregrip. Possibly 3.55 gears? Not sure yet, what do you guys think. I don't drag race it, maybe I will once but it's mostly street & highway...