My apologies for being too brief - my newbie status is showing:
It's a 1987 Cannondale SR400 "Team Comp" road bike. The previous owner upgraded the drive train to Shimano 600 SIS, so it now looks more like an SR600. The brakes in question are DiaCompe side-pull calipers, mounted to the front of the fork via a bolt from behind, with a nut and an acorn-style jam nut on top.
It is forever uncentered. It's a two piece caliper, so tightening the mounting bolt also puts too much friction on the fulcrum point of the two caliper halves and it binds them together. Loosening the bolt allows the whole caliper to swivel too much to one side, resulting in brake pad drag when off the brakes.
If I replace the whole fork with a more modern one (the original is a lugged-up steel thing), does that allow me to mount a modern brake more easily?
Thanks for the help, folks.