If you insist on mixing then use the specialists in each area i.e Simplex gears, Dia-Compe brakes, Stronglight cranks, etc.
Pretty much the route I took when I built the Ribble up, especially as it actually has to work (I do local TTs on it) rather than just look pretty. Campag for shifters (I like mine integrated and Ergopower ones look better and in my hands are more "intuitive" than Shimano), Sachs for derailleurs, Stronglight for crankset and headset, Look pedals, etc. For similar reasons it's not an out & out retro build.
My CX bike is even more "pick & mix", but then 'cross machines tend to be like that due to the battering they get - definitely not a case of "form over function"!
"Not so much a religion as a savings club for people who think Star Trek's a documentary"
- Marcus Brigstocke on Scientology