Exhaust leak

Slantsix.org probably has more opinions, but my method in the pre-internet days when we had to wing it, was to snug the nuts at the head, but not tight, then snug, the 3 crossover bolts, and keep repeating until all were at factory torque. Seems that would allow all surfaces to align. One time, I sat both manifolds faces on a perfectly flat optical table as I snugged in, though that only works if the head was similarly flat. I did occasionally get leaks at the cross-over and recall using 2 metal gaskets once.