It makes total sense that they would have redesigned the casting back in 1960 to build some research and development models for the DDC before going into full production in 1963. Don't know why that didn't occur to me. Guess I'm used to the car part numbers where the decade and year usually refer to the first model year the part was used. I'm sure there was more development time allowed on the SOS DDC, especially after their ORC debacle. Thanks Sean.
This has been an interesting thread. Didn't think it would create so many responses. Thanks everyone.