The "southren,poorboy,carolina"type iron monted gun is one of the most "easy" to work up.
Any rifle requires study if you want to get it right. As far as "easy", the only easy kits I know of are the factory kits like the Lyman and Traditions offerings and even these can be challenge.
I've have one of Dennis' parts set now and it's going to make a fine rifle. I would not call it easy though. I do not have one but I know folks who have built one, but a Chambers kit/parts set, though expensive is probably the easiest to assemble of the parts sets.
The following is the main factor in a Southern Mountain without the unnecessary furniture.
Architecture
Architecture
Architecture
Since they are so plain this has to be right to have a great Southern Appalachian rifle.
The same is true with any rifle, the architecture
has to be right as it is the heart of the rifle, but that has to be near perfect on a Southern Mountain.
It's true the Appalachian rifles are built sometimes without a butt plate but honestly, I do not know if this makes them easier or not.
Since it has no plate, the butt has to be shaped in a pleasing, user friendly manner that still matches the architecture of the rest of the rifle. Here you are working against the end grain and honestly fitting a plate may be easier when it is all said and done.
One thing about the Sitting Fox is the butt is not right, the builder needs to study originals to get that down.
Another big one is the lock choice. A Southern Mountain should have an English lock like JD suggests. The Track offering also comes with the incorrect Siler.
I guess what I mean about a plain southern rifle is that it is still a longrifle, only more so.
Honestly, if the OP wants a cheap and easy shooter that he can complete with sandpaper, here you go.
Link Traditions Kentucky
I'm not meaning to be negative but building a rifle from a parts set requires an investment in time tools and effort. Mostly effort.