I currently have the EGR disconnected, and don’t have an emissions diagram. My car didn’t have/come with the head mounted vacuum amplifier and I can’t find a diagram for the slants without them.
There's one in the shop manual.
AFAIK '73 just had the sticker with the timing info etc, not the full diagram.
Of course a Calif car might have something different.
I would think the EGR valve is normally closed and only opened whith enough air going through the venturi and the temperatures warm enough.