Your best bet may be just universal belts from Summit or Jegs, or any of a number of other places that cater to street rods and such. The best bet to figure out the size is just to measure, get some string or a flexible sewing type measuring tape and connect the points you decide for anchors and with you in the seat strap it out. Give it 4-6 more inches when you order so you have some room to grow, or so others can be assured to fit too should they need to drive/ride in it. I only mention the "give some extra room" part because I'm a big guy, but I can fit pretty much any stock seat belt, but when it comes to some of the universal stuff skinny people put into their hot rods it can get embarrassing to have to say, "oh, I can't seem to fit". lol :nanawrench: