I have them in my "Marriage Licenses of Frederick County Maryland: 1778-1810" by Margaret E Myers. They were married, or at least had their license given, on 21 Jan 1807.
I also have a will for a James Castle Sr from 31 Mar 1845, the executors were James E and John A Castle. The will is in book GME-3-31. I couldn't find anything on them in the tombstone book.
There is a Castle book in the Historical Society, not sure how good it is though.