I used some cheap parts house "cherry bomb" glasspacks as the only muffs on a truck DD. they worked but did get louder over time. In their favor was that they did not neck down where the end nipples are welded to the main case & the louvers were punched outward, both for no restriction. In your case I would get the longest pair I could find or even 2 pair of em with or with out some dynomax regular type muffs. best would be a quiet restricted system with some electric or vac or cable cutouts right at the header collectors, not cheap tho & would be quiet when you need quiet & loud only when you want it.