[400TT]

You can insert some homemade custom spirals into the centre of the muffler. Something to make the exhaust gas work and get more optimally silenced by the muffler. You can make tripod supports at end of the spirals and attach to inside of muffler tube.

If you want to go the steel wool route, you need to make baffle plates with holes in it to support and trap the steel wool. You can make them with a tab that is supported by bolt or screw. You drill a hole in the exhaust pipe, inserted you baffle plate and secure it with a screw through the tab. You will want the coarse steel wool from hardware shop and plenty of it, packed pretty hard. It is amazing what exhaust gas will travel through.

A little trial and error will get you there.