Hi Busted......welcome to TFF!
Wow! You've got me drooling on my keyboard! What a beautiful Kentucky/Pennsylvania flintlock rifle.
You might also want to post this on our "BLACK POWDER SHOOTING / MUZZLELOADERS / HANDGUNS" Forum: http://www.thefirearmsforum.com/forumdisplay.php?f=17
Here's another resource you might try: http://frontierfolk.org/ky-lr.htm
I know relatively little about blackpowder arms, so I can only tell you two things about your rifle.....
When it was made....the eagle design is what's known as an "early Federal eagle", so that would place it after
1790, and probably before
I don't know who "H. Koch" was, but I can
tell you that he might have pronounced his name in one of three ways...."Kotsch", "Cook", or "Coke" (my mother-in-law's maiden name was Koch, and various members of her extended family pronounce it in those various ways).
Also, Koch being a German name, there's a pretty good chance your rifle was made in the Pennsylvania area which had (and still has) a large German population.
And lastly, at the risk of giving our business to a competitor, you might want to try: http://forums.*********.com/forum.asp?FORUM_ID=2
The moderator there, Capt. Kirk, has a large computer database of early gunmakers. He may have some info on "H. Koch".