The input and comments have been fantastic! Thanks!
The Huret Duopar was a tremendous improvement over the previous derailleurs I owned, but it still had issues when shifting on a climb. The Deore line came out the next year and it seemed even better, but it drew criticisms from the local mechanics, "Hey! A derailleur with built-in slop!" He ate his words within a few months.
Smooth shifting under load was elusive in 1980, but I saw much better designs on the road as time passed. Lets go forward and build my bike to be the best it can with what we've got to work with.
Is there a Shimano, Sram, or Campy system known for the smoothest shifting?
With a 126mm dropout, what cluster should I use to enhance shifting performance?