Earlier and Later mean various things, when applied to various Stovebolt engines. With respect to exhaust manifolds, it typically refers to the "down pipe" from the manifold going straight down (all 216s, and 235s from 41-49 (I think)).
1950 and newer 235s and all 261s had a "down pipe" that was angled towards the rear.
I think that there were similar year-differences in the intake manifold port diameters. However, I think that all 216s used the same intake/exhaust manifolds - these might have even changed by shops/owners over the years.
