UPDATE....
The State of Alabama Archives has really helped us on this.
What I have been able to figure out.
The gun is a later period Birmingham made (tombstone proofed) English shotgun, single barrel that originally had a flat tailed English lock. It may have been flint as a breech bolster with drum does not quite have the same patina as the rest of the barrel. A smaller percussion lock with a round tail has been fitted in the bigger mortise. It looks like the original lock was over 5 inches. I think the closet made lock would be the Davis Twig with the tail filed flat. Their late flint with the flat tail is about the same size as the percussion lock presently on the gun.
This gun looks to have a hooked breech with a single key. The gun is a halfstock with a single wedding band transition on the barrel. It has a grooved iron underib with the pipes missing. The nose cap is missing but the entry pipe still exists. The buttplate is missing and was missing in it's years of use. The butt has worn smooth and the mortise on the comb was filled with a piece of wood shaped and nailed in place to fill it. This work along with the lock replacement is very crude.
Update to the update...
As 54Ball said, the Alabama State Archives have been extremely helpful and so has Travis. Much appreciation to them and the rest of you who have chimed in on my project.
With all the information, suggestions and research leads that have come forth I have refined my initial plans for my project. I am going to try and replicate GGGranddaddy's fowler as closely as possible to it's original appearance. Some searching around the web have turned up most of the appropriate hardware. The only concession will be a rifled barrel vs his smoothbore.
As 54Ball pointed out, the original flintlock was about 5 inches and flat tailed which agrees with the pictures and measurements that Alabama provided. I had considered the R.E Davis late Ketland lock but it is a little short of 5 inches, so I think the Twigg lock "bobtailed" flat will be a good fit and probably as close to what the original lock was. From Track's description and what I've read R.E. Davis makes a decent lock.
I have drawn up a rough working plan (over a TOW Issac Haines Lancaster plan) and it looks like this will be a doable project for my first build. Actual measurements and photos are close matches. And Track has a fowler stock available with only an undersized barrel channel and a full ramrod drill. No other inletting has been done and it is available in walnut as the original. It is a fullstock so no problem for me to cut it back to a half stock and my LOP is about 13 1/3 inches so I have plenty of wood for inletting the buttplate. It has about a 4 inch line-of-sight drop (vs 3" on the Issac Haines) but the drop seems to match what I see and estimate in my photos. (TOW also recommends the Twigg lock as a good lock choice)
NOW an important question for the experts: Colerain makes a 44" octagon-to-round rifled barrel in both .54 & .58 cal which fit perfectly into my plan. The only thing I am concerned about is the profile description says there is a slight flare at the muzzle (about .063" over the last 5"). Since this is a half stock I will have to use an under barrel rib per the original gun. Will there be a problem installing the rib and/or the ramrod tubes? Should I just plan on ending the rib a couple of inches short of the muzzle?
Suggestions or experiences needed.
Thanks