If the OP wanted to go to 700c and the brakes don't reach, drop bolts could be used. (A fitting that goes into the bike frame's brake bolt holes and that you attach the brake to a little lower down. I've never used one and haven't seen one in a long time (when it really didn't matter to me) so I cannot give you any details. Just that they do exist and can be made and allow short reach brakes to reach low rims or longer reach brakes to reach at shorter and more powerful brake pad locations.

A Duck-Duck or Google might turn up a source or at least a picture.