You quoted 1801-5 proof marks if these are correct then the trigger guard would have been pineapple finial ,the one on the gun has a acanthus finial which is from the 1750-60 period , the trigger is more of the 1800 period but the ramrod pipe is also much earlier and would have been steel and not brass . The side plate is also from the 1750-60 period and is more for a Fowler if a trade gun it would have been a flat serpentine also the buttplate with a broad tang , the 1800 period had a narrow tang Finally the barrel if 1800 would have had a hooked breech for a Fowler the method of the proof marks suggest to me an import of foreign iron barrel with maybe a Ketland proof mark.
If the 1800-05 proof marks are correct then you have a gun built from early parts .If the proof marks are wrong then I would say the gun is more to the 1750-60 period I would personally favour the latter, I maybe wrong but from the images that is my opinion of the gun
Feltwad