Are you certain that the Weinmann 610s are too short? If what I've read is correct, you only need an extra 4mm of reach to go from 27" to 700c wheels, which ain't much (4mm is about 5/32"). On my '74 Raleigh Record, the 610s have about 10mm of slot available if I want to go to 700c. However, your fork and brake bridge geometry may be different.

You will lose some "squeeze" with the brake pads moved out to the ends of the brake arms. I upgraded from the old Weinmann levers/Dia Compe extensions to some Tektro 200A "high mechanical advantage" levers, which help quite a bit. I priced long reach brakes and decided to limit my upgrade to brake levers, keeping the centerpulls and the 27" wheels. I figure I'll be OK as long as I can find 27" tires.

Good Luck,

tcpasley