Got around to putting the manifolds back on with new gaskets and hardware all around. It all went back together easily enough so the next time any part of the exhaust has to come off should be a simpler affair with a lot less colourful language.
I thought it would be rude not to fire it up with the u bends disconnected just to see what a straight piped flat 6 sounds like. It's a nasty, snarling, popping and very very loud. This was few blips to only 3k as I'd need ear muffs to go higher.
Also the blow is gone so wonder what I will hear next now that my focus on that issue is gone???
https://youtu.be/_GVLTgNWGLc