I had visited the Chrysler foundry in Indianapolis several times, V8 blocks would be cast 2 at a time.
And I have 30+ years experience at the IH / Navistar foundry in Indy. Concerning the numbers seen on the outside of the casting close to the part number, those are Pattern numbers. Patterns 1 & 2 would run together, patterns 3 & 4 would run together and so forth.
Concerning why one would see a pattern 4 with an early cast date. It is because when launching a new engine the foundry would would require that more than one set of tooling be available. That is so Patterns 1 & 2 could be in production use for a day or two, then they would be returned to the Pattern shop for routine maintenance and Patterns 3 & 4 would be in use for a day or two, typically two sets of patterns are rotated, as they wear beyond normal repair, patterns 5 & 6 and 7 & 8 would be brought in.
Concerning dimensional improvements, I would not say that later ( higher) numbered patterns are better than earlier ( lower ) patterns. Break through improvements in dimensional accuracy are more closely related to improvements in the core making process and in how the cores are processed and are assembled into a complete package. It is the unusual case when a single engine remains in production long enough for it to be re tooled with completely different core making processes. The slant six is one that comes to mind. The slants up to the late 60’s were oil sand cored, after that they were hot box, the final series in the 80’s were cold box. Those charges tie closely to the 3 distinct slant six cylinder head varieties.
The core boxes are similar to patterns, in that they are also identified with numbers. The lower numbers are early the higher numbers are later, with multiple numbers ( core boxes) being in production at any point in time to allow for repair and maintenance.
