I finally implemented the belt-as-seat-strap idea that I got from a post made by nj1639.
The existing seat strap on the Splendid RustBucket was in good condition, and I wanted to use it on a 1973 seat I restored, hence the need for this braided leather belt strap.
The tongue end of the belt is braided back on itself (hard to see, but it's there on the top belt end in the pic), so all I had to do to it was fold it over and secure it. The other end of the belt was stabilized using JB Weld that I dyed black, and then ground smooth after curing.
The fastener is a Binding Screw (AKA a Chicago Screw in a recent thread).
The red arrow points to a hidden metal bolster inside the folded-over strap. I had to enlarge the screw hole in it just a tad to accept the Binding Screw.
https://www.mcmaster.com/99637A311/
This is the Binding Screw that I used. I came up with the Binding Screw to replace the BIG rivet idea two years ago, which Is when I bought them, for $2.66 each. They are now $4.02 each.
The belt was $5.75 from AliExpress. Be sure to get one that is 3.5cm wide. The first belt I bought was too wide to fit in the mounting bracket's slot.
Comparison. Not a bad substitute for that impossible-to-find original rivet. (I used a rusty washer under the Binding screw to match the Sensational RustBucket's patina.) Also, the thickness of the Binding Screw I used was a little skimpy, so I had to use very thin washers. You could always buy longer Binding Screws and trim them to fit.
My only regret, is that I should have bought a
Brown belt. It would have looked funkier, and would have picked up the gold stripe on the tank.
I've got about 500 miles on this strap, and it looks just like it did when I put it on.