FWIW, I had what I thought was a manifold or head pipe leak on the passenger side and tightened everything down I could find. While the head pipe/manifold connection was a bit loose, cranking that down did not help the noise or exhaust gas situation.
What I finally traced it to was the stamped steel cup that sits in the intake manifold and surrounds the choke thermostat. That gasket was wasted and exhaust from the intake manifold choke preheat (crossover) passage was leaking past the gasket.
I wound up getting a new steel cup and gasket, (the original cup was okay, but they frequently rust out) and installed it with some copper RTV. I let it set up a couple of days and when I lit it off the next time, it was totally quiet. It might be something worth checking out.
I was not interested in blocking off the crossover, as I want to keep a stock set up. In fact, I still have a functional manifold hot air stove along with functional snorkel flaps, so the whole thing works as intended.
