How is '54 Yblock (239) water pump different than all later ones?

[Daves55Sedan]

For that matter, the '54, 239 heads and intake manifold are also not singularly interchangeable with the later Y-blocks, but it is possible to install all three mating parts on a later short block.
The 239 car engine heads have smaller intake ports spaced a little bit closer together than all the later Y-blocks.