Newer one is from 1929. Older one is just odd. serial number is 7599. It doesn't have the large bobbin plate, even though the treadle base is cut for that. It has a smaller slider plate. The thread take bar looks the same, but is shorter on the older one. They have different top tension wheels. Faceplates interchange but that short tension takeup bar bangs against it on the bottom stroke. And I am totally unfamiliar with Whites, so I can't decide if there's a part mismatch or if I just don't have it set up right. I was going to try and buy a bobbin and case for the newer head, but now I'm concerned that I'll wind up with a part that won't fit.