RE: Engine ID help
A lot of people leave the exhaust gasket off as the softer gasket material tends to compress and then the mufflers screws come loose on you.
The Pitts style mufflers like on your engine are quite common. Several companies make them too.
Many people converted them over to use the modern CDI ignition modules. No fuss no mess going that route, plus you get to pull off some of the heavy items on the front of the engine too.
Walbro seems to have made something like 10,000 different carbs. Mostly it is the jet sizes and bore size is the main difference. Different manufacturers would order carbs to their specs for a engine and get a special part number assigned, so that the carb would be for their particular engine. Helps make people buy parts from you that way.