I chased a flooding issue and actually measured the "holding power" of the inlet valve on my QJ (69 Buick 7029240) as taught by Cliff. I measured 12 psi to overpower it... quite a bit higher than 7.
My copy of the 1970 Service Manual has this interesting note:
So at least for 1970, 7 psi was "within spec" for a mechanical pump with a return line/vent.
I don't know if the float, needle, and seat were "weaker" in 1968 but I doubt it.
Several members in other posts have warned variations in pressure will raise or lower the fuel level in the bowl, but I don't know how sensitive carb tuning could be to that variation. Those with knowledge can address that risk.
Mike