I replaced the Altus derailleurs and shifters on my '81 Voyageur 11.8 with Ultegra FD-6603 and RD-6500 (long cage) and old Suntour barcons. I converted to a 700c wheelset with a Shimano 3N-80 dynamo hub in front and 105 in the rear with an 8 speed SRAM cassette. I used Tektro R365 calipers (nutted version) and immediately replaced the stock shoes with Kool Stops in the back and VO shoes in the front. I am very happy with the setup.
miamijim's advice is good if you continue to use the original wheelset.