[jbarron]

Big question is "Do you need the 31 spline axles".
If I was doing this again I would just get a Mustang axle.
I prefer the centered chunk and I think the length is a better fit.
The '99-01 explorer axle in mine will not take most "used" modern offset wheels and fit under the bed without a tub. Limits the selection of off the shelf wheels or craigslist finds that would look good.
I currently have my frame sitting on a set of borrowed Mustang wheels and the tire is ~1/2" from frame rail.

Take the measurements first and see what axle fits your needs keeping in mind what wheels you want to run and what offset they come in.