I'm going to bring this topic back to life.
Joe (ssl78396) shared pictures of these headers with me.
Here are a set of Bill Thomas C1 Corvette big block headers. Verified by the catalog pages from a 1969 Bill Thomas catalog.
Congrats again Joe on the great find.
I wish they were hanging on my garage wall.
I will let Joe fill any missing details from here.
Thanks,
Marty