A few things that came to mind while reading
-I believe the seat bolts are Torx T55+ ("plus") size, not a T57 (but as you noted a T55 will work in a pinch). Also I think my era may just have hex headed nuts on both (but like yours, rear are studs and front has the whole thing come out). I get a little confused because I did a lot of work on my buddy's 2003 chassis Ford Class C RV (I think that's the one with the T55+).
-Aren't those old Singers great? I have my mother's 1953 (I must be a bit older than you
-What I wish I could buy is the Ford part that was the standard vinyl flooring for the base cargo van. In other words it's heavy vinyl the same shape as the front carpet. I have looked and looked and never found it for separate purchase as a Ford "part" (not going to buy a whole new cargo van just to get it
-My carpet is still pretty nice (previous grampa owner had plastic over EVERYTHING), so I kind of did the opposite (and much easier) of cutting some of those interlocking "puzzle piece" foam sheets and laid them over the carpet. But I'm saving this tutorial in my memory bank.
-I did help my buddy remove and replace the front carpet in his 2003 E-450. We first put down some pieces of self-stick Sound down type stuff (although brand was Second Skin). This is the butyl-y type layer that only needs like 30% coverage. Then we used another foamy sound product - I can't remember any of the names now, darnit. Unlike you though, he wanted vinyl and was in a hurry, so we used some vinyl on a roll from a hardware store (so of course it had seams). Meh.
- Lastly (and why do I think you already have a pending tutorial on this?
BG
PS: What I *really* want to see is what's going on in the back?!? I see "guts"

