I would swap components, taking the best of the Voyageur and putting them on the Passage since the paint is in great shape on the Passage. Put the DiaComp 981's, the Super Mod 58's wheels, front and rear derailleur, (but the Huret Shifters were very good shifters, maybe the best made, so leave those on the Passage), the seat post is a toss up, I like the fluted look but others don't so it's up to you; and move those items to the Voyageur unless their worn out of course. The rest I wouldn't bother with. I don't usually like butchering an all stock bike but your keeping it for yourself and the paint on the Voyageur you said is rough so your not going to be able to sell it for much.
Also on those older cantilever brakes, they work stiff from the factory, if you replace the cables with better cables they work a lot better...at least they did on mine.
Side Note:
I own a 1985 Schwinn Le Tour Luxe, they shared the same frame as the regular Voyageur, the Passage was not made in 85 only 86. The 1985 Schwinn Le Tour was the best year for the Luxe, all other years saw a degrading of the frame used. They only made the Luxe for 3 years, in 1983 and 84 the frame was cheap unnamed 4130 cromoly while the regular Voyageur used Champion. The 86 Passage used the same frame as the 85 Luxe but the 85 Luxe used a better Suntour Mountech derailleur system vs the Huret Duopar that couldn't match the gear range the Mountech could making the Mountech more suitable for touring and off road use, and the Duopar was more delicate; in addition, finding old Duopar's are a pain and expensive while the Mountech would be far less expensive to find, but the Mountech had problems with their pulley wheels wearing out too fast but supposedly they fixed the issue with the 85 models.