John,
If you search for "John Thomas flintlock rifle" on the first link Elnathan gives for the Royal Collection, there are two color photos of this rifle on their website, and this is all they have for photos. You can then enlarge and get a pretty good look at its current condition. The photos plus a careful read of George Shumway's description are as close as we can get - plus looking at the rifle on display, if you can. I've contacted these folks regarding their Oerter smooth rifle, and they have no more photos or notes than what is on their website now. Unfortunately they cannot find the photos and records they had in 1980, and shared with George.
Egg replaced the forend with walnut - so no forend cap remaining. The wire around patchbox is silver, you can see this in photo and George mentioned that in his description. Egg replaced the original double triggers with a single set trigger, slid the trigger guard forward, removed sideplate and spliced in wood, supposedly browned the barrel but it and lock are now bright, made a new ramrod and so on. The rifle may have been damaged - as he straightened the barrel and replaced the forend, etc.? The barrel now is held by keys with heads. On the Oerter smooth rifle, Egg put some sort of clear finish over the areas he disturbed, and perhaps over the entire rifle. He may have done that here, as well. But the color you see on the remaining curly maple on their website is probably close to the original, as Egg does not appear to have stained or messed with the wood.
If you can enlarge the photos and guess at size of wood spliced in around the new lock, it may give an idea of the size of the original lock, which George says was larger than Egg's replacement. Good luck and please share what you learn and what you do. Bob