26" 1 1/4 wheels (used up to 1950s) ETRO is 597 vs 700c at 622, so circa 12mm difference to adjust brakes, and taking into account difference of tyre used on 26" - 32mm vs say 25mm you can get for 700c wheels, than the total difference is only 5mm. So you can use modern wheels on the bike, which gives lots of tyre options you don't have on the old ones