I just picked up a circa 1990 race bike. 25.3mm Vittoria rear (measured) fits with paper clearance at the brake bridge. (Thin cardboard? No way!) I'm running 24c front and rear. Super short Cyclone calipers with the pads pushed all the way up to center on Open Pro brake tracks. One, sweet, sweet ride! Love it! (It does have more room for fingers under the DT and behind the ST than the Fuji Pro I raced in the late '70s. Still, I've jammed my fingers several times reaching down to shift and so far have remembered to use my Fuji caution and reach for the seatstay first when I reach back to wipe the tire.)
And with that, I'll leave you all and go start building the sewup wheels that belong on it (and see if I can go 25c tubbie or if I have to stick to 23c, I think my old sewup standard though in those days, I never saw a tire width posted (on the tire, on the package or anywhere else. Pretty sure the Criterium Setas I raced were about 21c, but again, no documentation.