Exhaust Pros/Cons for Slant 6

There are a least 3 distinct manifolds, They deal with the choke housing differences and reinforcements along the manifold. In 1976 the manifold started to have a 5* cant to the outlet. I believe this was to allow for a larger exhaust pipe to clear the pan rail. A larger head pipe may have been used for cars that needed catalytic converters.

I have never seen a 2 1/4" pipe nor a manifold with an exhaust opening larger then 1 7/8". And I have 5 of them sitting in my workshop.