Joined: Dec 2011
Posts: 2,519
Likes: 18
From: Fort Worth, Texas
Bikes: 2000 Bianchi Veloce, '88 Schwinn Prologue, '90 Bianchi Volpe,'94 Yokota Grizzly Peak, Yokota Enterprise, '16 Diamondback Haanjo, '91 Bianchi Boardwalk, Ellsworth cruiser
B66 is for double rail, while the B67 fits the more common single rail clamps. Photos I am finding of that model show it with both types. If the bike dates from when you believe, it is probably a single rail clamp. Maybe.