swapping early 3.09 1st into later case

Yes, it can be done and that is what I ran for years in my 71 Duster behind my 440. I also plan to run that same trans behind my 500 in my Barracuda, at least until I get a chance to install my T56. My best friend built it for me. He did exactly that, took the 3.09 from the early trans and put it in the late case.