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Adding to Lynn's good advice above, exhaust leaks are best checked w/ engine cold as some disappear when engines warm up.
Have you tried removing the belts and running the engine for a moment without WP/Alt etc turning as this may help isolate whether they may be the problem or not?
Another thing to try is disconnecting each plug lead individually one by one w/ engine running to see if the sound changes...this sometimes helps indicate which cyl. has the problem as you're removing detonation from the cyl. and they're now only rotating.
Doubtful w/ a fresh engine but sometimes listening at the tailpipe and carb w/ air cleaner removed helps indicate bad valves...exhaust valve if TP noise and Intake if @ carb.
Great to hear you're getting closer to taking the Stagers for a rip!
Please say hello for me also LMK when it's happening as there's a small chance I may be able to drop by on one of my trips to/from Woodstock as I'm usually there about once a month.
~ Pete
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