Topgun;
I think that several guns have surfaced with the large hook but with the cross pin cut out as you describe. Its function as the check hook was actually eliminated with introduction of the small hook gun but it was retained & served to cam the extractors on the small hook guns. AS LAC did offer to upgrade to the later actions when one surfaces such as this it is really near impossible to say if it was built that way or upgraded. Either way it is most likely "Factory".
On the single hook guns the lug pin reaching the end of the slot in the hook serves as a very efficient check. Be interesting to see which Mark's is.
