If the rim is a standard width of the era (~19-20mm external), then I can suggest a few tires. Continental GP5000 28s will measure closer to 25-26mm wide as will Compass/Rene Herse 28s. I'd imagine Gatorskins run smaller than advertised as well. Soma Supple Vitesse, etc.

I made a Bead Width while laid Flat chart to help me in this tire madness. About 67mm between beads, with the tire laid flat/out, will net a ~26mm external width once inflated (at about 70-75 psi).