Well, while his isn't strictly an AMA rule, there is a rule in AHRMA that restricts shock length. If you're riding in the "vintage" class (which is 1974 and older) you can't have more than X inches of travel front and rear. As it turns out, there's only ONE bike that this applies to, and that's Maico's big bad forward-mounted-shock thing that started the long-travel revolution. In the name of keeping things fair you have to put shims on your Maico's shocks. Running a stock Maico against a stock anything else is, officially, cheating.