On my other T, I used four 3/8" bolts, big flat washers, spacers and nylocks. Ran the bolt through the washer, body, a spacer, the frame, a washer and put the nut on the end. Done. My other T was in a wreck and the body didn't come off. This stuff isn't hard and if you're trying to prevent the body from coming loose or off in a very hard hit, as in the above pic, good luck. These cars will practically blow apart, in a decent wreck. Drive safe and keep your mind on what you're doing, but keep in mind, these cars are just a motorcycle that won't fall over and they're made of glass. You get hit by anything doing more than 45mph, well.......
A guy at a show told me, "All you're trying to do, is have an open casket funeral, if you ever get hit hard." Had to agree. Here's a pic from my wreck. The cop car made an illegal left turn and caught me on my wheel and tire. He was probably doing 15-20mph. If he had hit the body, it probably would have snapped in half. Towrads the rear and the body would have cracked and possibly ruptured the gas tank.
Oh and don't bring seat belts into the mix. As I've stated before, if I get hit in one of these things, I'd rather get thrown out.