The Dickert is a good choice for the time period you are after. I would place the average Dickert kit cica 1790. Things can be done to back date it a little or move it into the 19th century if you wish. For example I personally would have no problems with a later Dickert having a straight barrel and a smaller bore. It may not be true to an actual late Dickert but it is true to the era. Now for an earlier Dickert a swamped barrel with a larger bore is more correct. 50 caliber is a good middle ground.
Many other types are available to the time period, Like Armstrong, Beck, Gillespies and others.
Bore size has to do with two things large game and wild Indians. If you research you will find that while the deer skin trade and Indian war parties were in full swing in the east, rifle calibers tended to be larger. As the deer, buffalo and bear were killed off in the east and the Indians assimilated or moved west, calibers tended to get smaller for small game like rabbit and squirrel. Hence the rise of the shot gun as the southeastern gun of choice for generations. Larger calibers were not unknown in the Appalachians and were useful for hawg killins and the occasional bar hunt. Out west were the buffalo, grizzly, Comanche, Cheyenne and Sioux were to be encountered, calibers were larger like the earlier guns in the east.
The most important thing is research if you want a historically accurate piece. If you have the knowledge of whats right and what you want you can "contract out" your build.
For example you want a close copy of RCA # whatever. It is a possible Revolutionary Virginia piece with a simple domed patchbox, 46" swamped barrel in about .54 caliber with an English Daykin lock. It has simple but good carving. No known maker and no parts kit is available for this piece.
Step one find the components. You may ot find the exact item but many parts are close enough. The Daykin English lock is not reproduced but the early Ketland is which the Daykin was a copy. A barrel supplier like Getz, Rice or Colerain may have a 46" barrel available. A stock supplier has a blank long enough and a pattern that closely matches the original. early Lancaster is close enough.
Step 2 ... You have researched, compared and found parts that are as close as possible. You send the barrel to a stocker who has the blank and pattern to set or inlet your barrel and drill the ramrod. You then send the barrel off to have the lugs and sights installed.
Step 3... You find a builder or stocker to inlet the lock, butt plate triggers ect.
Step ... 4 You find another builder to shape and carve.
You may know of another builder who offers a PC finish you want so you send it to them for the final finish.
You act as the contractor it is done a little at a time and paid for along the way. It is defiantly your rifle as you were the main component in its creation. Doing this takes research and lots of contacts plus maybe a friendship or two.