This may only pertain to the MX line of seats, but has anybody had reason to replace the grip bars that are pop riveted onto the fiberglass backer that hold the upholstery in place? 

  

I need to do a new cover on my MX360, but haven’t dug into it that far. Subscribing to see what pops up!

I posted the same thing on the Facebook Vintage Yamaha MX and YZ group, one guy says get some scrap metal and snip some out. It has merit but with the metal not having its full width like the original, I think it may have issues bending the tabs back down flat. Then again....

I did find something. They are called metal upholstery tack strips. they actually are everywhere on the internet. The only ones I can find are the kind with the "points" going in the wrong direction. I would think they would need to be twisted to get them to function the same way as the originals. Then that would not let them lay as flat as needed to keep them from mashing down on the frame members that the seat rest on??

The Facebook group has 2 leads, one is an online offering, hvccycle.net/alligator-strip/  
The other, one of the members made a die to cut the V notches in a metal strip. He had a photo of some that he done with the rusty original with it. Quite the nice looking product, better than the  one from HVCcycle in my opinion. I PM'ed the guy to see what he wants for a strip.

I saw that awhile ago and was going to mention that. Glad you saw it too.

I didn't know these existed so I made one of these myself for a 79 DT100 except I didn't have a die to cut the tabs. I used a chisel on a block of wood to cut each tab by hand. The bottom edge of the seat pan was fairly rusty all around so, starting with a 1" piece of sheet metal flashing, I bent the flashing in half using a vice and shaped it over seat pan so it made a smooth edge with the tabs on the inside edge and ran stainless pop rivets from the outside edge in. I had to cut a few reliefs in certain places to deal with the contour of the seat pan but, while a bit rough, it worked fine and was largely hidden by the seat material. Just goes to show you everything we think we invent, some else has appeared on shark tank beforehand.