I did some more searching around and found one shop with a right side and chainwheels only, no left arm, I got the right side for $40. I found another shop with just a left side, and another set of just the arms, I bought the whole lot for $20 cash. The only problem now is that the right side arm I bought don't match either of the other two left arms, and the second Right arm that came with the second set without chainrings has a lot of shop wear on the right arm.
The finish is different on these, the first one has sort of a polished look, the one left arm looks more like a brushed finish, and the arm that came with the second set is thinner? The crank axle end isn't as beefy looking.
All are date coded CH, CI, and CL, making them all from the end of 1978. Could they have changed styles every month? I have to go Sat. to another shop who says he's got two new right sides but no left arms.
How on earth did these shops end up with so many partial sets? The one shop had a shelf full of right side only arms of all types, no left arms. If the chainrings and arms were one piece I'd understand it as it would be a wear item but all of these had bolt on rings. (Of course I asked about tires in the one shop and they didn't have a pair of any tires either). The one shop said to just use any 170mm arm, it won't matter. I'd hate to see a bike they worked on.
I would have figured that Shimano parts would be fairly common, but I find far more high end stuff than I do Shimano. Lots of old Campy and French parts but not a lot of 600 stuff.