#3 is double nutted as a test a few min before taking that video. The stud looked a little chewed up right where the manifold meets it and the nut also loos a little chewed so I put another nut as a "spacer" to try and tighten the nut on some fresher threads
ah ok, thanks, that explains that!
if nuts are all snug and no signs of carbon escape, then I'd say the flange is good.
what about the manifold itself, no slight crack a little lower down?
(though your 71 will have the good 2 piece manifold, less prone to cracking than the later USA one piece restrictive piece)
I'd still adjust timing chain, if you haven't done it on this new to you spider.
Our twin cams seem to transmit noise and it's hard to pin point the source. A loose chain can be noisy.
....maybe check the compression in cylinders to rule out anything odd there that might have happened after your italian tune up
: all plugs out, hot engine, wide open throttle.
(edit) oh, sorry, it wasn't you who did this, it was shuga....got myself mixed up!