Depends of course on the Retrobike....
Discs outbrake anything else, period.
My RC200 F6 is my only concession to discs on a bike that goes in the 97 and earlier thread. But none of my other "97 and earlier" bikes are getting used at the moment, with the exception of the Parkpre whích gets the occasional airing.
Consider maguras. You get most of the "feel" of discs without having to ruin your frame. And the blocks last reasonably well.