Boy do you have an interesting engine!
The big O with 48 in the center, between the distributor and breather tube, was used on 1948 and 1949 216 engines.
The casting date is a bit of a mystery.
Even if someone bought a replacement engine in lets say 1950 (the casting date) I would think you would get a 1950 engine with out the 48 in the circle.
Has me scratching my head.
