Jani,
Casting date would, and should, precede production date. In other words, the block could be cast in January of '66, then machined and engine assembled in March, two months later. Probably means you have a '66 engine.

Could be this engine came from a truck which had the larger pan too, or someone added the larger pan for some reason.

As for "collar", you said cam shaft, but probably meant crank shaft. I can't tell well enough as the picture shows on my screen, but I see you have it circled. If there is a "collar" inserted, that would be the pilot bushing/bearing for the manual transmission input shaft.

.010 is what we call a clean up bore. Adds just over 1 cubic inch. In another thread, Mike had mentioned a .125 overbore (1/8 inch) to get a 283 up to 301 cubic inches. That would be 18 cubic inches. .010 is about 1/12th of .125, 1/12th of 18 = 1.5".

Power pack was Chevrolet's designation for engines equipped with 4 barrel carb and dual exhaust.