"Maryland Longrifles" by Hartzler/Whisker is another good book for Armstrongs, expensive if you can find a copy, but maybe a library loan. Lots of pics of different JA guns, plus many of his students.
Some things in addition to Smartdog's comments that jump out, just in relation to Armstrong...back end of the stock shape just looks a bit off, more Ohioish/later percussion to me than Armstrong. Comb nose a bit too sharp, cheek a bit too wide front to back, maybe needs more wood off the bottom of the stock from the wrist a ways back? Hard to tell for sure just from pics though. An Armstrong needs carving, period, he didn't make plain guns. PB release needs to be in the toeplate, never seen a JA with release in the buttplate comb.
Last one is nothing on you, but I hate those precut Armstrong patchbox kits, they always look too small on the gun too my eye.