Looking at my 70's Avatar there is a mix of Campag, Shimano, Suzue, Sugino, Tange, Kyokuoto.........and the rest
Careful Shaun, you'll be giving some of your fellow forum members apoplexy with comments like that.
SNight: I know nothing about older road bikes, but if you look at modern production bikes, it is common for certain components to be used in order to get the complete bike to a 'price point', the worst offender currently is Boardman where you can see a right mish-mash of parts.
With custom mtb's in the 80's and 90's, it was also common to have maybe Ritchey brakes and levers and then Campag or Shimano shifters and mechs, this was usually down to a combination of budget, practicality and weight.
"Try not to punch any clowns"