I haven't been able to think about anything but that rifle since last Sunday! I hope somebody buys it and makes it easy for me. I have learned a lot from both Sinner and 470 evans. I've been fooling around with double rifles for about 18 years now, but always boxlocks in no way near this price level or quality. The whole business is frightening! I saw the markings on the barrel as far as the load, and also saw that the flats were marked "450 EX". I also knew that the NP marks didn't come out until 1904, so I just assumed there would be no indications as to nitro, period.
Reading between the lines, so to speak, is 470 evans is saying it could be a BP gun that was re-engraved to show the nitro load, or it could have been a nitro for black gun? If so, this would surely cut the value at least by half, if not more. If there is possible damage to the carriage, as noted by Sinner, can a good gunsmith restabilize the action so that it doesn't shift? I'm guessing the damage is caused by the lockplates moving during recoil.
There is a "funny" Rigby here in San Antonio at Bass Pro Shop that purports to be a 7x57R. It is a rising bite sidelock in very nice condition, but something just wasn't right. I e-mailed Paul Roberts who informed me they never made a rifle in such caliber. I returned to the store and asked to examine the rifle. The barrels are replacement barrels made in Ferlach. They didn't know this--they say--and are asking--ready? $49,999! I understand the original records are in the wrong hands so what are we left to do?

Thanks guys for the valuable information!