I love these old engines and used some of them back in the day. But if you intend to use one for regular flying, you'd be better served using a modern engine. a modern engine will give you far better service. If you are just into the novelty of using an old engine and the fun of getting one going again, more power to you!! Many carbs can be mated to the engine with a bit of ingenuity but will probably require some machining. For both carbs and mufflers, Ebay sources for OS, Enya and other brands can yield some useful parts that can be adapted to the McCoy. As stated earlier, many strap on mufflers from the late 60's into the 70's should work well. On your original question, I have no idea what the thread size is for the venturi but you'll learn quickly as you start adapting parts. Have fun!