The '73 should still be one that is either all on or off, the metering ones were used in the early feedback cars, or the ones with electronic fuel control. You have to be careful with vacuum line setup if using a later metered power valve, if not careful you think you have PV operating but it's not. Better to have the earlier on/off one anyway.
Look at the valve and seat, immediately obvious which is which, the on/off one simply uncovers a hole, the other one does it gradually with a long tapered valve there. If running hi-perf stuff you could burn some pistons running the metered one. IIRC, the metered one does not have a metering jet lower down in the passage, by itself it is the jet. The on/off one there is a lower metering orifice down in the hole further, the hole closed on/off is NOT the restriction there.