Concerning originals, the more I study the less I know.
American Longrifles have been built for three centuries. In that time a multitude of styles and combinations or similarities of parts and styles has been done. It's all been done before. Some were successful, some not so successful.
So if you are looking for a historical example for "whatever?" chances are you will find it.
For you or any aspiring builder you need to decide now what kind of builder you want to be. Do you want to build kind of, sort of stuff or educate yourself, take the steps, gain the skill and build the real thing?
I'm not talking about Rococo carving, exquisite engraving, silver moons and hunting stars, I'm taking about architecture. All the fluff can come later. Architecture is what makes a rifle greater than the sum of it's parts.
How do you want your rifle to be judged, Wow! nice investment cast sideplate or Wow!! now that's a rifle?
Now you can use parts like that for your build. They should accent a great rifle not be the accent.
Here's a neat old rifle. This rifle was built with musket parts that dictated the heavy wrist but the overall architecture is great. This rifle looks robust but if you read the specs it's quite dainty.
http://americanlongrifles.org/forum/index.php?topic=4165.0 Here is a Penn rifle plain as a piece of bread but wow!
http://americanlongrifles.org/forum/index.php?topic=2636.0 This rifle is a lesson on architecture. You won't find much better. IMHO Mathew was the best of The Gillespies and one of the best longrifle makers period.
http://americanlongrifles.org/forum/index.php?topic=8015.0 Here is a pleasant rifle note the profound architecture.
http://americanlongrifles.org/forum/index.php?topic=9317.0 Another architecture lesson
http://americanlongrifles.org/forum/index.php?topic=24728.0 Then there's this guy.
http://americanlongrifles.org/forum/index.php?topic=24724.0http://americanlongrifles.org/forum/index.php?topic=13729.0 I hope I have shown that decoration is just that, decoration and it's the real rifle underneath that counts. A mix of parts can be used to build a great rifle, but it's the rifle...not the parts.
It must work and function very well. It needs to have good architecture, anything else is gravy.