RE: OS .15 Steel Fin?
I feel it is a mistake to remove the baffle of an articulated baffle throttle engine and try to make it function with some muffler. Remember also to start using muffler pressure with the carburator intended for 100% suction supply (venturi's for suction supply carbs are considerably smaller than those intended for combined suction/muffler pressure supply.
If noise is not a problem I would urge you to use the engine unmodified.
Here is my little OS pet .10 articulated baffle throttle engine that has worked great in my Aero 9 remake for some years now.
John