If it's an A&M I would keep it. You can get a muffler for the 5.8 from Bisson, JA Engineering, and others. I would go ahead and order a muffler using "Brison 5.8" for an engine description to make things easier in ordering.

BTW, Makita/Dolmar bought out the Sachs cylinder line, and I have no doubt that yours is a Sachs based design.