I gave it all another quick clean of brake cleaner and blew it all out with an airline. Buttoned it all back together with new gaskets and hardware. I also used some ceramic high temp grease on the hardware. It will be interesting bro see if it makes any difference in future. It's also inert or so the story goes so should reduce the galvanic corrosion process between the steel and aluminium but then again who believes the marketing waffle anyway. It's rated for up to 1500C so I suppose time will tell. I keep an eye on the torque just in case it does cause any issues.
I was curious to hear a straight piped flat 6 so I fired it up without the u bends and all I can say is it's loud. It's a distinctive sound. Snarling and popping. I had a mic on the camera and I think it even got overwhelmed with the range and pitch. An interesting experiment all the same.
Any all is back together and the blow is gone. Now I await the next oddball sound that I'll latch on to and torment me into doing something else.
Although if I left it straight piped I might not hear anything again. Here's a sample for your aural pleasure or not!
https://youtu.be/_GVLTgNWGLc
Onto the next job now - new stat and water pump.