That gun has a lot of charm. There are a lot of subtleties to stepped wrist architecture and when the best makers get it right it looks really cool.
Everybody has their own take on what they read into these guns, but when I first saw that Jack Brooks gun it brought to mind a reference I have seen to the Christians Spring shop stocking a rifle for a "Shawanoe" chief in the 1750s. And also some past posts (I think by Dan Phariss) about references to the Shawnees having, and being proficient with, rifles in the 1750s-60s. I was wondering if that was sort of Jack's concept - maybe a rifle made for a native who had an old English tradegun that was brought in and restocked with a rifle barrel. On the other hand, a rifle stocked up with parts that include pieces of a traded or captured tradegun is the other way you could go with it. Either way, I love pieces like this that sort of tell a story.
On the locks, the English vs. Germanic lock issue has been over generalized, in my opinion, especially when it comes to early guns. Like Rich pointed out, English locks turn up on early Pennsylvania guns, just not as frequently, and you see Germanic style locks on many Shenandoah Valley guns made up through the early Golden Age period. There are very, very few definitively attributed southern rifles from the pre-golden age period. We know they were being made, and there are many pieces that are possible or likely and are presented under the assumption of being southern in the books, but we just don't have as many signed examples by makers documented to be working "where and when" as you do from Pennsylvania. To further confuse things, some pieces that have been in the collectors' and museum worlds for a long time were reconverted many years ago with parts that were not necessarily representative of what was there originally.
Guy