Update:
I saw this rifle being carried around at the Raleigh show a few weeks ago. I got the seller's contact info, and through his patience, I was able to sell another rifle in order to fund this. I called Allen, who lives fairly close, and I made plans to stop by with the rifle and let him tell me as much as he feels like sharing about his rifle building days.
All the metal furniture is made of German silver, and the barrel is a Douglas XX, 1" x 40". The lock is a Davis (with the circle-D) mark. It's a hefty rifle, but not unmanageable.
I think it has a base design along the lines of an eastern Pennsylvania rifle, though Allen admitted on the phone that he often made whatever he felt like making at the time, without any strict adherence to a particular design.