I bought a complete rear end out of a 67 firebird. It was the same as my 67. I have kept the original with factory 256 geared non posi in storage. The one I bought I changed to 355 gears with a auburn posi unit, and new axles. For what my original 326 engine slighly modified, it does great on the street, but going down the highway, it's another story. rpms are up there at 60 mph. It all depends on alot of major factors. First off what do you plan on doing? Srip car? street cruiser? maybe the all elusive best of both worlds? What ever you choose, you need to consider the total package of what you want to do. do some research first before you jump into the mix. You will be ahead of the game and a little lighter in the pocket