I once packed a Kerker 4-into-1 muffler on a 1982 Nighthawk with fiberglass. For that, it was as simple as removing the endcap, sliding out the baffle, tying the fiberglass matt around the baffle, and putting it all back together. I got the packing from Dennis Kirk. I don't know how similar the Mac exhaust is to the Kerker,though. It did make the sound much more desirable for me (I prefer quieter exhaust noise).