RE: Fuel for old engines
That's rare and hard to get muffler, George. I believe that is the same muffler that will fit both of my OS Max .10 RC cross scavenge engines. Fortunately I live where mufflers are not mandatory at the RC field outside of town. On those, the exhaust baffle coupled with carburetor throttle barrel is sufficient.
I've got the later OS Max .15 RC with muffler cross scavenge engine, which is the one you mention that uses a steel cylinder insert.