Before reading any of this....

I built (if you can call it that ) a mouse can after muffler using, coincidentally, the exact same Mouse can pictured in post 9.
The can cost a wooping $1.33 (CDN no less). I used some cheap, hardware store, copper tubing. Total cost - less than $2.

I used Martin Hepplers software as well. My mousse can is setup as a simple exansion chamber, but I built a couple of others (other types of can's - but the mousse is nicest) setup as high frequency band stop filters to test as well.
The expansion chamber has very low attenuation at multiples of it's own resonant frequence. I tried to set it up so that these did not align with multiples of the engine's firing rate at max throttle.

I have a OS46FX with a Jett Stream muffler that generated about 100 dB at 9 feet, 90 dB at 20 ft. Not crazy, but a bit too loud for mixed company.

I'll get the mousse muffled dB measurements and let you know how it worked.

My long term solution is a Mac's quiet pipe. As a quick work around the mouse can is great. It may find a permanent home on another plane.

(It was quieter, when I tried it it, but it certainly didn't seem as quiet as I expected based on the reduction predicted by the software. Took away about 500 rpm.)