Some engines can be fitted with strap-on type mufflers. There were OEM strap type mufflers as well as some aftermarket units from various manufacturers. If you can list off the engines you’re looking to add mufflers to, someone could point you into a direction to fix up at least some of them. The little guys in the .049-.074 size can be tricky as some cannot be retrofitted with a muffler while others can. Pictures would be helpful on the little ones especially, but any of them pictured would help with finding solutions for also.