On the drivers side valve cover, the high stand off wire loom, has a hole in it, unlike the 71's that do not have this hole. I think the intent was a plastic piece inserted into this hole, held the idle stop solenoid wire.
The 72 and VERY early 73 340 valve covers are fairly unique, but can also be found on the 72 318 engine with electronic ignition.
On a side note, by 1973 the 318 and 340 valve covers are the same.
Check out this link, it helped me, but it is not entirely correct, there are some minor errors.
http://books.google.com/books?id=phKNxZn...p;q&f=false