The "- #" is the casting core box number. Core boxes were used dozens of times, and when it needed touchups, or a production change was made, the core box number was changed "up". There is no correlation between that number, and production dates, or the quality of the iron used, or the quality of the casting process.
In terms of info - on the 340 block, just below the left hand cylinder deck surface (basically where the power steering pump goes) should be a series of numbers stamped into it. That tells you what assembly it is, and I think what body it went into, and what factory.
