I was incorrect. They are cold rolled steel.
I did not do a raised bead around the ports. The flanges were flat when I installed them. All of the bolt holes are over sized to prevent the studs and bolts from breaking. I do have studs wherever possible. It makes things MUCH easier to assemble. An early B engine compartment is pretty tight, especially with the later B K-frame.

I have tried a variety of normal exhaust gaskets as well as solid copper. The Cometics are next on my list.

It seems that exhaust leaks are a way of life for me.