[Oldsguy]

I drive a '69 Delta, 455 engine, TH400, 2.73:1 rear. The car turns 2150 rpm at 70 miles per hour. The car could handle 3.73:1 or even higher but the trade off would be higher rpm at the same highway speeds. For the 455 I have decided 3.73:1 would be as high as I want to go. A 350 wouldn't mind the constant higher rpm as much as a 455 so you need to consider that. Also, my carrier is a type O 12 bolt, not the same as the GM corporate 12 bolt. I have been told it is a little more difficult to find ring and pinion sets to fit it. I am not sure what type carrier the '73 Delta had but of course you would have to get ring and pinion sets to fit whatever carrier it was. There is some info over at Realoldspower.com if you do a search and prepare to read a lot of posts you will find some good info. Try using key words like "type O", "12 bolt", "ratio", etc. Good luck to you both.