1967-68 Pontiac Q-jets (Rochester or Carter) did not use the POE-system, but they uses a larger float assembly with less leverage on inlet needle than used in 1969 and later units.
The vertical slots in primary bores are the off-idle slots, the horizontal slot is used for controlling the ignition vacuum advance, if itīs located above throttle blade with .040" of the off-idle slots shown itīs a "ported" source used on 1968 and later units.
If the slot is located under the throttle blade (on 1967 Carter aftermarket replacement units) it is a manifold vacuum source, wich is correct for 1967.
Original 1967 units did not use the horizontal slot in bore, they uses a source from beneith throttle plate.
I think your unit will be fine properly adjusted.
Red = 1969-70 POE, Yellow = "Regular" :
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