I finally got around to actually doing this resize project.
Because .308 Marlin Express brass is not available yet, I called Hornady and asked them if resizing 307 Win. would work and they told me it "should". (no absolute yes lol)
I got the brass in today and resized it in my 308 Marlin die and then loaded 10 cartridges. They ran through perfectly so now I'm on my way to test fire.
Looking good though trimming is kind of a pain.