Well I tried out the Welting foot. It's a 5/8".
It worked perfectly the first time.!!! I tried various tension settings but fairly tight seemed the best. The seam is dead snug at the outside of the roll. Straight as can be. It didn't take very long at all to make both door windlaces. They look nice. I did a test fit on the car but I need just a little more trimming on the door frame so the windlace lays flatter. The fiberglas and wood bonding adhesive are not compatible with staples at all. They just flatten out. The windlace will have to be glued on and the ply-grip strips will need some #4 or #6 flathead sheetmetal screws about 3/8 or 1/2 inch long. I have some stainless ones ordered. It will be tedious to put all those little screws in. They will require pre-drilling or they will just bore a hole with no threads. Already tried it. I tried self drilling screws too but they don't work either.
I also got some headliner material to practice with. It's just a light gray with a soft foam backing. I had to adjust the tension again...looser so it doesn't gather the stuff up. It works good now. The seam is nice and tight and the material lays flat. Just a slight curve to the final product.
I think you said earlier that I won't need a listing on it as I will be stapling it to the roof bows rather than hanging the headliner on rods. I did find some material that has a little stretch to it that is pretty tough. It looks like it might strengthen the seam. Maybe it's not really necessary.
I did manage to sew my finger a week or so ago. For a small wound it sure did sting.!!! The needle just barely touched the finger bone then completed the stitch and pulled it tight then ripped it out...or I ripped it out yanking my finger back. ouch, dang that hurt. talk about bleed!!!