The Zeus 2000 brakes were oddly enough weight weenie stuff. Silly light for centerpulls. They are cool for sure but between the short reach and the slender caliper arms, they wouldn't be my first choice for touring. They were very rare in the US. GC450 were spec'd on a few bikes so they do come up. If you are patient I'm sure you can score a set. Do they have enough reach for you? Might not be so happy with fenders. The original GC610 are somewhat more common on ebay, and probably more appropriate. Nothin wrong with Mafac either, and they are easy to find.

FWIW. no affiliation of course. centerpull brakes gran comp | eBay