it appears the cut-out for the horn is wider than the horn thus leaving a couple narrow openings each side of the horn. Is this then considered the way they vented the speaker within the design?

All of Altecs enclosures that followed this muddled model are really from the time when pre-TS parameters were codified ( early-mid 1970s ).

The "large horn cut-out approach is not the way to deal with the realities of tuning a Bass Reflex enclosure.

Again, it's an obsolete approach.