Hi Nate!
It's funny, but I've spent literally months making up my mind on how rear axle I wanted to use on my '37.
I was leaning towards Ford 9", but at the last minute I came across a deal on a Jag IRS. As some of the other guys have said, some of the considerations you need to make are whether or not you're trying to keep it stock (or close to), what sort of power train you're going to use (especially keep horsepower in mind), and what sort of ultimate use you have in mind for your truck.
You can modify most Ford, Chevy, & Mopar axles to use your leaf springs, but you'll need to invest in brackets to mount shocks. Ride height is also limited with the stock springs (if your plan includes lowering).
As you go shopping, take a tape measure with you and compare the width of the donor axles.
Good hunting!
