I have been looking for posi 2.56:1 or 2.73:1 gears for a 77-81 rear end for years so I can finsih my 500 project in a 82 Fleetwood. I tried runnng 2.28:1 for awhile and it is a bit high for the rpm range I'm running in. I am now running 3.42:1 which is too low. The car is over 3000 rpm on the freeway. I am about ready to pitch this rearend and try something else, but I really wanted to try to keep everything Cadillac. Basically I'm looking for someone to turn my on to some parts. I have a posi 2.29:1 setup if anyones interested, also a open 3.42:1 setup. Thanks

I have a 81 sedan deville with a fuel injected 472.. I started out with a open 2.41 rear... I felt I needed a posi and got one out of a 78 deville.. It , like yours had the 2.28 ratio.. That carrier can work with 2.28, 2.41 and 2.56 gears... you could go lower with a spacer ring... I was going to go with a 2.73 with a spacer ring but could not find the 2.73's... I ended up finding a set of 2.56.... I am glad I ended up with the 2.56 gears..at 60mph its about 2k rpm..
I also built a switch pitch trans that works well with that ratio...