Thanks for the information! According to the 1967 Ford Shop Manual, there is indeed a right and left rocker assembly, designated by marks on the rocker arm shafts. However, I suspect these marks were only provided to eliminate the exact problem I ran into.... which one can from which bank. :-)
When you talk about performing the adjustments when the valves begin to open, how can you tell? I mean, I'm underneath the car with a wrench turning the engine over my hand.... I cannot physically see the valve train as I turn the engine over. Even if I could, the valves move so very little that I just cannot conceive how a person can tell when they *just* begin to open. If the engine turned over easily and I could see the valves at the same time I was turning the wrench, I could perhaps see this as possible. But, even with the plugs removed the freshly rebuilt 390 turns over very hard and I cannot obtain access to the nut on the main pulley from the top side.... I have to crawl underneath the car.