Okay, well, did a quick Google and answered my question about Harper's Ferry - not.
Not so fast, Take a look at at the Southern Boys rifle.
http://americanlongrifles.org/forum/index.php?topic=4161.0 The above rifle inspired me to use an American/military styled lock on my Gillespie build.
Re Davis Contract lock with a goose neck cock, one is offered with a more military double throat. This is basically their M-1803 rifle lock without the markings.
Mock up on a Mathew Gillespie stock.
Roughed out and tail reshaped, it's going to work out very very well.
Here is original a Southern rifle with a Ketland and Co lock.
http://americanlongrifles.org/forum/index.php?topic=11592.0 This rifle possibly dates to the 1790s and might be a few years older. So this confirms a Chambers late Ketland as an excellent choice. As the 19th Century progresses many makers copied the Ketland for their no name locks, so thats another reason the Ketland is a good choice.
Many styles of those no name or American importer marked "hardware store" locks are not accurately reproduced today again about the closest is the Chambers Ketland which many were copied from.
The Bailes, Durs Egg and Mantons while English and a much better choice in style than say a Siler were really not found on Southern rifles. Those high end English locks were usually found on English pistols and fowlers. The Bailes/Manton are about the same size as many of those mentioned no name locks that are not produced today. The Ketland tends to be a little larger as it is a little earlier than most southern flinters. Some say that the Chambers Ketland Design dates to the 1770s-80s. Keep in mind that's when it was state of the art. It was produced and copies were made for many decades.
I know that was clear as mud.
One last thought.... many of the locks you see on Southern rifles may have really been percussion. Many also may have been flint, converted and then converted back and a few may have had a flintlock lock plate that the lock was converted to percussion and the rifle was built new as percussion with a flint plate.