I'm having 2 sets of 321ss by 3/8 inch thick exhaust flanges made for my turbo project.  I always have 2 of most things made as I change things or just screw things up the first time.  I'm using the pattern from the steel flange that I got from Mazdatrix, but am not using the web between the port flanges and am making them just big enough for the 2 bolts above the port and the one hole below.  So a set of flanges will be one right and one left that will be identically and the center one that is smaller.  I have the same setup with my existing engine and it works fine.  Yes, I know there are 304ss flanges out there, but welding 321 pipes to 321 flanges is better.  If anyone needs a set or two, let me know.  I don't know the prices, but these water jets guys have done work for me before and are fair and accurate.

Don Walker
N113BR, Renesis, 24 hours in the air