I was hoping to get some new insights here, but it does not seem to be forthcoming so I'll answer my own questions.
63mini may be referring to the timing lever and I don't know what else.
From what I've learned;
When mech parts were plated, Mills used cad plating; SEGA used nickel. I don't know if I could tell the difference from a photo.
SEGA used the same part numbers as Mills, at least while they were distributing and revamping Mills slots.
However, there is notable differences in what they stamped or did not stamp.
Mech part numbers are usually little or no help in dating a machine.
The difference between a Mills mechanism and a SEGA is usually apparent from the operating fork.
The Three Crown machines first came out in 1957 and apparently did not have a long production run.
Vintage slot machines are very often found with replacement parts or entire mechanisms swapped out.