I have a pair of Gran Compe fitted to my old 1955 James Fothergill which was updated in the 1970's and they are extremely good for their day, the red pad compound appears to be very good indeed, I wish I could find some replacements.
I use them on rides around the Derbyshire Peak District and as yet they have'nt scared me!
Saw a KHS (Japanese bike) Mixte Grand Sport today, had the Dia Compe's on there. I think as bike makers moved to the Pacific Rim, a lot of those bikes, maybe even low budget ones got Dia Compe's on them. The things you learn. I'll bet when people say they have a Japanese vintage bike, it's often got Dia Compe brakes on them and I'll bet there are examples on this website.
I once scoped out a Japanese advertisement from the '70s for my own porpoises, as a project I researched Japanese bikes.
Kind of awesome isn't it.
Zebrakenko, Bridgestone, Miyata, Nishiki, etc. I'll bet there is a load of Dia Compe's that they used.