[70Supreme]

Question:

I have a 1970 Cutlass Supreme with the "o" type 12 bolt differential & and a 2.60 gear. I want to increase that to a 3.42 gear with Posi. Is that possible with off the shelf parts? Anyone with some practical experience who would be willing to post some options, I would appreciate it.
Later upgrade will probably include a trans with overdrive.

Thank you