In my opinion, it is definitely not off of a garden tractor. I'm thinking that it might be for a 5000 series Grazer but I'm too unmotivated to track that down. :sidelaugh: :sidelaugh:
If someone was re-powering their tractor with a twin and needed a muffler to make a custom exhaust system, that's a cheap start. Cut off the pipes near the flanges and then fabricate exhaust pipes to hook the engine to the muffler.