Hey Dale,
I don't have the referenced book in front of me and I'm not real familiar with Mr. Groves work, but I think you'll find a lot of the Maryland rifles were heavily influenced by York County builders. That only goes to reason given the close distance involved. Even Armstrong rifles show evidence of this. Quite a few of the Maryland rifles had a York style butt piece and trigger guard. Also, I've seen the Floir-de-lease (sp?) design used around the tang and rear ram rod thimble, the same one made so famous by Mr. Schroyer of York County.
Having said all that, I'm thinking you might consider using the measurements and architecture of the Groves rifle and use the York influence, and/or other Maryland builders, to guide you with the other details since you're not doing a copy. As far as the tang shape goes, you'll find that all the examples you listed were used. I. Haines had a big influence in the area and Lancaster's not that far from Hagerstown. I'd say that probably has something to do with the Haines style carving.
I don't have Reeves number in front of me either, sorry. If someone else doesn't chime in, I can get it for you. About two months ago I spoke to Reeves about Armstrong furniture. He had a pattern for the TG and butt piece but hadn't cast anything. Don't know if that would be what you're looking for or not... TOW just came out with some new Armstrong castings as well... Hope that helps some.
Ed