Thank you all for the continued comments.
I have been comparing my rifle to photos of two other Pendrill built guns I found photos of on the internet. The first is a breechloader in the NRA Museum, the other a fowler sold out of Canada posted on Guns International. I would say that both are undoubtedly by made by the same gunmaker that made the metal parts for my rifle. I think that the stock of my rifle is based on the original as the overall stock architecture of my gun follows similar lines to the NRA gun. The details, are obviously different, particularly in the execution. I am unsure of the period of the restocking, but I tend to believe it was done recently based on the condition of the holes in the brasswork, those wtill being bright, and undimmed by tarnish.
NRA Museum rifle
Guns International fowler
The engraving styles are remarkably similar on all three. Here is the buttplate for example:
NRA Museum's buttplate engraving
Pendrill Fowler posted on Guns International
My rifle's buttplate engraving
Regarding the tail pipe construction. I believe that the tailpipe was also constructed by Mr. Pendrill in the mid 1700's using a formed pipe, and a cast tail, as shown by Smart Dog. Comparison to the photo of the NRA museum's tailpipe shows there to be an almost identical pipe on that rifle.
NRA Museum tail pipe
enlarged
My rifle's tail pipe
More pipe details
Note the engraving style is in keeping with the butt plate, and it is in keeping with the rest of the gun. Probably done by the same engraver.
The shiny new pin hole is evident, along with the much smaller original pin hole.
The trigger is offset to the right. The left side of the slot seems to be set on the stock center-line.
Mike