Good Morning, this is George McAllister
I believe your revolver is a early transition model. The barrel is from a 1861 Old Model, the rest of the gun looks like it's a 1858 New Model. The markings are government inspector marks that were stamped as the gun was being manufactured. I couldn't tell of there was a cartouche on the left grip, but I'll bet there is. Your pictures are great and really help, thanks for adding them to your post. If you're not a member of the RSA, we'd sure appreciate it if you'd consider joining.
Be In Touch,
George
GBA