To answer Fingers' ... the hammer is not "light" but there is no problem cocking it with that slightly bobbed hammer spur. It cocks very smoothly.
I'm adding three more photos in this post - mainly to highlight the TRULY weird thing about this gun ...and it's not immmediately obvious
As you can see in the closeup of the hammer, it has been lightened with three holes - the spur has been bobbed just a hair, and it looks like the front of the hammer may have been re-shaped. You can also see some very pretty wood in the grips ...and the brass Philips fastener that holds them together. The fit of the right hand grip panel is a bit off, especially right at the butt. I found a Phillips screwdriver that fir that grip screw properly and carefully removed the grips today ... whereupon I discovered a serial number stamped into the frame that matches the 3 digit number on the barrel .... this gun's serial number is the mid 400's !
So - have you Whitney or Spiller and Burr fans spotted the TRULY weird thing about this gun? Study the frame in front of the cylinder in the first and second photos (close up right side, and full left side view) - notice the screw for the catch for the base pin is on the LEFT side of the gun instead of on the RIGHT, like it is in every Whitney picture I've ever seen? Yep - someone, sometime, converted this into a left-handed target Whitney.
Look at the third photo, which shows the trigger guard. Notice where some material has been removed on the left side? The trigger itself has also been slightly re-shaped to ease shooting it with the left hand. I may be forced to work on my left handed shooting with this gun. If you look sharp at the trigger guard photo, you can also see where it's been drilled and tapped with a small hole that probably used to hold a set-screw to prevent over travel on the trigger.
A few other notes - the barrel measures in at 7 1/2 inches with my tape measure. Fortunately, I had a tin of Number 11 caps that I bought by mistake a year or so ago (I'd saved them as last resort caps for my Remmies), and they fit perfectly. The cylinder, as you can see, shows know signs of the "safety notches" found on the current Pietta Spiller and Burr, and also seen in photos of the old Palmetto Whitney (thanks to AntiqueSled Man for posting that old DGW flyer.) Given what Fingers said about the double diamonds being an older maker's mark, it's likely that the safety notches were a later feature in Whitney repros.
I was able to pop caps on all six chambers - the bobbed hammer took some getting used to, but once I did get used to it, it's smooth and easy to cock. The trigger is light, and crisp, but not hair trigger light. But, the combination of my big hands and the rather small trigger guard means I have to concentrate and use strict trigger discipline to avoid firing prematurely, and gloves are right out.
It's supposed to be nearly 50 outside tomorrow, and I plan on taking her out to my small berm with a light 15 grain charge under a wonder wad and .375 Hornady swaged ball and seeing how she handles making smoke again. Because there are no safety notches, I'll be loading all six, but only capping on the line. We'll see how she does at 25 yards.