Mopar Small Block Head info:

308 head was the only head to barrow design enhancements from the prior development of the w2.. Because the 302 has the same exhaust port variety it always had from the intro of the 318la.
The 302 and all 318 heads have basically 3 intake port designs and 3 exh ports before the magnum predecessor.

#315 1964-65 is laid back and ramps up 'as cast' with varying casting/core shift lending med to short exh short turns, slightly diff exh port window size and core thickness. They list a specific header gasket you can port match too on those and 920's. They are a closed heart'ish shape chamber.
#920 1966-67 'dice heads' by the 4 dot squares cast on the outside...very much the same as the early heads with but a slightly different closed chamber that was more or less edited from the previous.
#234 1967 truck/indst. These heads fearure very the 1st version of the 675 style int/exh ports and the same closed chamber as the 920 . The big difference with these heads is they have no exh heat cross over and instead flow water through a passage in the same location as the exhaust cross over would be that flows through the intake=water heated intake.
#675 1968 the brand new official passenger car head intake port, more blunt & bull nosed. Taller exhaust floors than previous 273 heads and were open chamber.
#593/163 air injection heads , they brought back the early laid back intake port from the 273 era, but even taller exhaust port floors. They were open chamber.
#302 closed chambers, 675 intake port and late #163 exhaust ports with air injection. The 163/593 is the open chamber twin to the 302 head and flows a hair better as cast without the chamber in the way.

Basically..Chrysler had a few port designs that differed in the intake short turns and exhaust ports. The early versions tended to peak higher but also mostly in the higher lift 'given the exact same work is done'.