Once you figure out how many, you could just line them up and put a spot weld on the edge of the stack to hold them.
That frame is such a mess, that you must be at the point of wondering if it would be best to start new
Yes building a new one and use the old one as design is Maybe the best way. But fixing an old frame has also something.
Sometimes, the fixing of and old frame is more fun than building a new one.