[FireSale]

As you said, the rules state that the distance between the backing plates can't be changed from stock (assuming we're talking a stocker). Later it states that a replacement rear end can be widened or narrowed to obtain that original distance. You can't bolt something on to do that so it's would be a machine shop task.

As for looking under other peoples cars, you need to make your own decisions as to whether to follow the rules or not.

Dale