Most of the restorers are used to restoring cars that have frames. Our Birds are no weaker because you take off the subframe. The body has it's frame built in. You put a lot more stress on the body when it's just sitting there on it's wheels than on a rotiss(unless it has frame connectors). The sub is like a big lever compared to the close attachment point of a rotiss. If you follow the logic that you need a brace to do floors then you should have a brace to do floors whether it's on the rotiss or not.