Wow. This is all really good info. And I really appreciate the different perspectives on this. You have all given me a lot to think about. Thanks again to everyone. I'm gonna look into putting the sbc aside and picking up a local guy who is selling a 318 / 727 combo. I've done so much with ford and chevy, why not dive in with some cool mopar stuff and learn something new. It would be cool to keep it all Mopar, I think I'm gonna add the v8 and auto, and then keep my eye out for a later model mopar rear end. I just got done working on a 49 gmc truck, and the one thing that killed me was trying to find parts and pieces for a rare eaton ho 72 rear end. I ended up getting a late model dana 70 (it's a 1 ton) and haven't looked back. And I plan on driving the plymouth, not looking at it, so serviceability is key.
I'll keep everyone updated with the project. I tend to get a little "obsessed" once I get a new project, so there should be lots to report.
Thanks again to everyone on the site for the thoughtful replies.
Brad