Mike-I have done what you want to do. I restored a Jacob Wigle rifle (Westmoreland Co., PA) that was found in a dry cave Indian burial near Vernal, Utah in the 1920's. It was originally a flintlock, probably built about 1820. The barrel is now 35.5" long, slightly tapered. But it was built with a 46" barrel, which I finally figured out on my third copy of it. That was the style in Westmoreland County back then. Your butt plate is probably Track of the Wolf's BP-MA-43-B, shown on my copies below. The patch box you will have to saw out and make the five-knuckle hinge, easy to do. The trigger guard will probably be Track's TG-MD-1-B. What you might think is a wear plate covering a misdrilled ramrod hole is original to the rifle, the fashion then. You can select rod pipes from Track's catalog. The barrel may well have been cut off and might have been up to 46" long. Who knows what the flintlock might have been. You just have to select one that seems to fit. Here is the rifle after I cleaned it up for the museum here.
Notice on the Westmoreland County rifle the sideplates extend past the hinge, which has 7 knuckles. This has a toe-line release to spring the latch, seen below the hinge. Jacob's brass work was beautiful. Here is my copy below the original, showing the trigger guard I referenced above.
I built three copies of the rifle. The maple one is the first, which I sold to Jacob's GGGgrandson in Ashland Co., Ohio. I also traveled to Jacob's Creek, PA in Westmoreland Co. to research him. The walnut copy is a .50 caliber for my cousin's husband, who is a Weigle. The third copy I built with a 15/16" by 44" barrel, and in doing that discovered from the pipe spacing that the original barrel was 46 inches long.
I could not tell from the inletting what the original lock had been, so I used a Jacob Dickert lock on the first copy, a Davis Early Contract lock on the walnut one and a Durrs Egg on the last one. The original rifle was about .38 to .40 caliber, muzzle too rusted to be certain. Both barrels I made 38" long, the first one .40 caliber and the second one .50 caliber. The third one is .40 caliber and 44" long. You will have to make the single trigger. You will need accurate tracings of the stock to duplicate it. It will probably have a short length of pull, Wigle's is 12.5 inches, with a lot of drop. If I can help you with any advice, feel free to ask.