I went to visit my Dad today and while in town there made contact with an old McCulloch dealer. I knew he had a good used 840 upstairs, so now it is in my hands.
Gear drive, 36" hardnose bar, 1/2" pitch chain, shaft mounted chain oiler driven off the sprocket shaft. Sound like just the saw AOD was looking for in another thread.
Same guy had the NIB 35A my brother bought, also has a NIB ProMac 800. Now both of us are thinking about how to resolve that situation. He also has a brand new 110 setting on the shelf, not sure it's ever been in wood but it has collected a little dust just sitting around.