dont run a paper filter they are the worst. Plus it won't drop to much horsepower. But yes the easist way is get a machicist to make you a "restrictor plate" well you got the m3? and that has what 6 intakes soo it might be kinda hard to make it for that. So i would go with the disk type muffler.

but dont go paper airfilter that just lets everything by pass your filter

-garrett