Im learnin' up on Indian trade rifles, not the Leman sort, which has been done about a zillion times, but something more along the line of a Derringer or other "off brand" make.
There doesn't seem to be a whole lot online specifically about these. Other than Lancaster style stock what other traits might these rifles have had? Plain or fancy, Etc.
Forgive me, but I have to chuckle about the part I've highlighted in red. My millennial son's first reaction is to "look it up on the internet" even though he knows most of the info out there is wrong and a good portion of the rest can't be trusted.
Not clear what time period you're interested in. Rifles traded to Indians began with the earliest rifles brought to the colonies--the jaeger. Some of the earliest records of American made longrifles show they were traded to the Indians. Colonial Lancaster rifles were so familiar to Indians in the Great Lakes region that during the Revolutionary War, the British government ordered English made copies of Kentucky rifles to give to their Indian allies during the war.
If you are interested in rifles from about 1800 to the cartridge era, you should order one of these books.
https://www.trackofthewolf.com/Categories/PartDetail.aspx/278/1/BOOK-RAI
It shows examples of rifles by John Guest, Jacob Dickert, Jacob Gumph, Christopher Gumph, Henry Gibbs, Jacob Dickert Gill, Jacob Fordney, Henry Leman, all from Lancaster, PA; John Krider, George Tryon, Edward Tryon, John Joseph Henry, Henry Deringer, all from Philadelphia; John Joseph Henry and James Henry of Boulton, PA; Martin Fry III of York County, PA; and several English made Indian trade rifles.
John Joseph Henry and Henry Deringer were born in the same year, 1786, in towns in the Lehigh River valley that were about seven miles apart (JJ Henry in Nazareth and Deringer in Easton, PA). They both made rifles with curved butt stocks showing their Lehigh roots. Actually, the Tryons and some of the Lancaster gunsmiths did, too. The curved butt stock was obviously a popular style on the frontier as well as the classic triangular butt stock of the Lancaster school.
Besides the different shaped butt stocks, there was considerable variation in patch boxes, side plates, and to a lessor degree, trigger guards.
Both government records and surviving fur company records show that higher grade, fine rifles were sometimes ordered. These included silver inlays on the cheekpiece and wrist and often some engraving. The plain brass-mounted rifles the US ordered from Deringer usually cost around $12.50 each. In 1811, the OIT ordered 12 rifles with silver bead [sight] "and stars or eagles on the breech" at $22.50 each--almost double the price of a plain rifle. In 1820, Deringer made them a "highly finished" rifle for $35. That was probably similar to some of Deringer's best civilian rifles like this one used in a famous duel in Washington, D.C.
(The full story on the duel and more pictures of the rifles used can be found here
http://americanhistory.si.edu/blog/pair-dueling-rifles-reveal-their-story )
One thing about the Indians guns after 1800, very few, if any, had carving on the stocks. Some had checkering on the wrists.
To really understand "what other traits might these rifles have had" you need to get the book linked above and study the photographs.