Depending upon the heads and cam config, I would guess that when new your engine would read as high as 170 psi.
Normal wear could reduce that to the 150 range; however your may have been 150 psi when new, again depends upon heads and cam. In this case, 135 would be normal wear. I just can't see a 43 year old engine still reading new engine compression in one cylinder.
The 122 however would be an expected number from an old, probably high mileage, engine. In any case, the range should be within 10 percent of all 8 readings.
How did you run you tests?
Best way is to bring it up to operating temps,
Pull all sparkplugs.
Disconnect the coil wire.
Remove the fuel pump relay.
Open the throttle max.
Crank the engine,
The gauge should climb in bumps, everytime the piston comes up on compression.
4 bumps will usually do it, but let it climb until it stops.
Jot down the readings.
Cylinder #1 is drivers side front, #2 is passenger side front.
If you still have a low reading, you need to do a wet test, this will point to worn rings, or valves.
Put a little oil in the low reading cylinder(s) and retest.
If the compression increases, the oil is sealing a bit of wear on the compression rings. If there is no change, the valves need attention. Worse case, there is a crack in the head.
EDIT:
@ryeder ,
@bsname just posted a good point that made me review the steps I provided.
And he is correct, the fuel will cause a problem, the fuel pump relay needs to be removed.
I will go back to my list and add this necessary step