Thanks Jim & Larry!
I'm definitely leaning towards the fact that the 72 340 valve covers did change in 1972. In 1972 they started stamping a hole in the drivers side high standoff wire loom, supposedly to secure the blue idle stop solenoid (ISS) wire. I have attached a photo of what it looks like. I'm trying to get better pictures of the plastic piece that inserts into this hole. I guess most guys just removed them, thinking it robbed them of horsepower like everything else.
As for the bend at the top of the wire loom holder, or it being completely straight... I think that throughout 1972 and the early part of 1973, the wire loom holder is straight, and for 1973 & 1974 the wire loom holder was curved on a 45degree angle, for reasons that are somewhat intuitive. Also, I'm certain that there is no difference in the valve covers for the 318 or 340 engines for 1973 & 1974 in that they have the high standoff wire loom holder on the drivers side valve cover. Further evidence of this can be found in pictures of the 318 & 340 engines in the dealership data books from 1973 found here;
http://www.hamtramck-historical.com/Now here is the real million dollar question... (Scott, you can chime in now)... could you have a drivers side valve cover in 1972, 1973, or 1974 with the low standoff wire loom holder on either the 318 or 340 engines? Maybe the 72 318 engine only? I don't think you could because the high wire loom was now serving an additional purpose; holding the ignition stop solenoid wire which required the high stand off wire loom. But I'm willing to hear the thoughts on this one. We are not quite finished yet!