How to quiet JCWhitney Dunstall type pipes?

[redblk63]

I like the look of these mufflers, but they are just too loud. They do have a vestigal insert, wrapped with what I take to be fiberglass material. Has anyone had any success making these mufflers a bit quieter, and if so, how?

Thanks,
Larry - Pasadena, CA, USA

[redblk63]

It looks like I may be the first to tackle this, so I'll report back if successful.