Scott
Wouldn't it make sense for someone to paint an engine just before installing.
If I were putting an over the counter block in back in the day, I would certainly have painted it.
I cant see the factory doing it..but then I wasn't there either.
The picture of your painted engine with the blue tag shows the rivet just resting against the tag like someone added it.
Those tags have always been available for sale if you look hard enough.
I know of two old school buses with about 15 'over the counter' blocks in their old wooden crates... 273, 318, 360, 361, 400's and none were painted.
Nor were the 340 or 440's that are gone now, painted.