How about chambered pipes instead of a muffler?
At some time during the 1960s my dad’s engine shop/auto parts store carried the AP line of exhaust parts. At one point he became a NAPA dealer, and converted to NAPA’s Soundmaster line. One of those suppliers provided a set of pipes to replace a vehicle’s exhaust pipe, muffler and tail pipe. There was no muffler, but the replacement pipes were crimped at several places, possibly forming chambers to cancel exhaust sound. When his delivery station wagon needed a new muffler, he installed a replacement “chambered pipe” set on the ’59 Chevrolet. The exhaust note was about the same as stock. Is anything like this still available?
You don’t really say what it is you’re trying to accomplish so I can’t give you very specific advice but I can say some general things. There are various companies that sell chambered exhaust pipes that can be used in place of a conventional muffler. Among them are Classic Chambered Exhaust in Milford, Michigan (classicchambered.com), and Sweet Thunder in Cadillac, Michigan (sweet-thunder.com).
Another option for you may be asmall-diameter round muffler. Most of the major exhaust component manufacturers offer round mufflers so you have plenty to choose from.
The factors that will likely determine what’s the best solution for you include size requirements, exhaust sound and price. If possible, you should buy a muffler made from good quality stainless steel so that it doesn’t rust away in a few years.
A less expensive alternative that still offers decent corrosion protection is “aluminized” carbon steel, which is regular steel that’s been coated with an aluminum alloy to inhibit rust.