I have the same b17 & VO seat post (2 bolt model) they had a issue with the top clamp on the older models cracking . They sent me a new top clamp at no cost . I also have the Carridice seat bag support mounted which eats up the rest of the seat rail. It's a tight fit but works well particularly with TALL frames & the Nelson bag (will not work on small/med frames ,bag will rub rear tire )
cheers