X or R blocks will have a designator cast into the RT front.
X
R
R1
R1A
R2
R3
R4
R5

The casting #s are virtually useless given the amounts of variations that were available. A couple of my R blocks have actual "P" part numbers die stamped on them, but I dont recall where at.

There are a few variants of W5s....post some more pics of the heads. Particularly the rocker lay-out and the ends of the heads.


The world of R blocks is a total rabbit hole. Chrysler screwed up more than a few. Ive seen them with undrilled oil galleys. I currently have 5 of them, including one of the ones that got sold with the wrong cam tunnel