The "casting" number won't really tell you anything.
You need the part number from the box, or just "know" what you are looking at.

The only what I would call "good" stage 6's were the Chapmans.
All the others are a crap shoot for qc issues.

The best of the non-Chapman heads were the last ones made, which were cast by the Zeus foundry. They have the word "Zeus" cast into the top of the head.

There have been tons of threads for stage 6 heads through the years...... Just do a search.

Unless they have already been professionally prepared, and are a super bargain...... There will be more cost effective options out there.

Heres a good place to start:

http://www.moparts.org/Tech/Archive/bb/33.html