My '72 parts book shows just one power steering bracket 9786903 for all '67-'69 PS-equipped V8 Pontiac models. I checked my '68 and it too has the open hole.

It appears to be a pathway for the '67 A.I.R. equipped engines to connect through the bracket cavity to a hole (plugged w/o A.I.R.) in the left head.

Here's a photo of the backside of it from The Parts Place: