Thanks for the photos Mike. Nice looking gun, I have to warn you though, another board member will be disappointed that it doesn't have platinum blow-out plugs. Apparently, he's quite the recycler!
You're going to probably have a heck of a time getting those percussion nipples removed. You can get new ones from Track of the Wolf for about $6/each. I have a proof mark directory but other board members are far better than me at reading between the lines when it comes to proof marks. However, you're correct, 12=12 gauge. I'm not sure what Hh means but I'm certain someone will know.
What are the bores like? How much does the gun and guns barrels weigh?
Steve