intake/exhaust mounting, what am I missing?

The question was related to the three fasteners that hold the intake to the exhaust manifold.
The center fastener on the exhaust manifold was a 5/16 bolt on the 1972 and earlier years.
1973 and latter used a 3/8 stud in that location.
Just curious about which exhaust manifold was being used.
The photos in post 8 answered that question.
Both manifolds are post 73.