I have 2 Spiller & Burrs, 2 digit sequential serial #s, from the first production run. I got them from a friend, deceased, who also had serial #1. He had an original which was sent to Italy to study. These have the double diamond stamp on the bottom of the grip frame. I always thought they were Pietas. If you have a Whitney that has that mark I can't understand how it has been lost to antiquity as the Whitney is a rather recent repop. I have been around C&B revolvers for about 40 years and don't remember any other Whitneys prior to the current one. It isn't listed in the 2001 Dixie catalog but it shows up in my 2007 catalog. They do not list a maker but a teammate has one and it is of indifferent quality.
I understand the Whitney shares a problem common to the S&B repros in that the grip is too close to the trigger guard. It is so close that the guard smacks your saluteing finger hard enough to become quite a distraction before the end of a 10 shot match even with 15-18 grain loads.