Hey Chris,
I too have the 55.1 with a 283 and mine is running through a TH350. I got my Ring and Pinion from West Coast Differentials. I am very happy with my new 3.38 gears, running 2300 RPM at 55 MPH, smooth and quiet. $300 R&P $150 install kit, $150 set up on the third member at a good gear shop. I saved a couple of $$ by taking apart the third member and cleaning everything before I took it in. They just had to put all the clean parts together with the install kit and set it up.
Good Luck,
Buddy
