OK.............
That rear header that has tubes 4,5,& 6 in one group was compressing the hell out of those water fittings. On a lark, I loosened it from the head this morning to see how far id have to space it off to get clearance. As I loosened the header bolts, it pushed itself off of the head.
It looks like I'd have to space it 1/4" to get the most minimal air gap.
I had a small piece of aluminum to confirm the required gap. I tightened the header against it, and there still appears to be maybe 1/16" between the tube and the fitting. Clearly I had binding going on, my down pipe transition popped off when I loosened the v band clamps as well.
Ironically, with that little piece wedged in there, the piece that goes on top that ties the two headers together lines up, and fits way better than it did.
So,..gee. I get to drill three big holes in a piece of aluminum plate, and use a jig saw to cut out the world's thickest header gasket today.....
CnC....plasma/water jet/ laser cut. PFFFT....I don’t need em.
I cut the existing header flange out of 1/2" plate with the same tools...aluminium should be a cake walk.