The muffler is a Bisson 'universal'. If you look closely you'll see the adaptor I fabricated between the exhaust stack and the muffler - it's made out of two pieces of sheet aluminum stock.

(Picture was taken prior to first engine runs. I quickly discovered an almost total lack of muffler pressure. So I bored out the muffler tap and soldered a short length of brass tube with the inside portion cut at a 45° angle facing the exhaust port. Better but not enough. So I wound up using a Perry pump which works just fine.

I believe the stock pressure tap position is where it is because the stack is much thicker than the oval section. But it's in the wrong location for generating adequate pressure...at least in my installation.)

Tony