(just my ideas; everybody has their opinions on dating early guns)
He'd have had a gun from anywhere in eastern PA. If you want to go back to 1760, consider guns that could have been made by Andreas Albrecht and others at Christian's Spring, Abraham Berlin, Johannes Moll, etc. Maybe Antes goes back that early; I have to think about that. Read Eric Kettenberg's articles on his website; they are a tremendous resource.
Guns to use as examples include:
The Musician's Rifle (there is not a complete set of photos and write-up on this one but EK built a rifle with many of it's characteristics
http://web.mac.com/kettenburgs/Site/1750s_Rifle.html and Wallace Gusler included a few photos in some of his Muzzle Blasts articles). This gun may be 1750's; it has a scratched in date 1756, I think.
The Marshall rifle, which may be over-represented among re-enactors, and is either a 1760's rifle or a restock of a 1760's rifle in many people's estimation. See Jim Chambers' kit.
The Deschler gun (see EK's articles), a cherry stocked, brass-barreled smooth rifle with a side-opening patchbox. Might need to back-date this one with a sliding wooden patchbox.
A gun in RCA (is it 17?) sometimes attributed to Antes. EK used this one as inspiration on one of his creations
http://web.mac.com/kettenburgs/Site/Early_Arms.html#6.
RCA 19 is probably from west of there, and maybe 1760's; it's a smooth rifle, walnut stocked, with a conglomeration of furniture and no hallmark features that can point to a maker or region.
RCA 40, sometimes related to the Christian's Spring guns, is a "transitional" piece with an open guard and heavy Germanic styling. The carving is not up to Moravian standards in my estimation, so I see a relationship but doubt it was made by the Moravian gunsmiths in Bethlehem.
There is a short rifle in RCA volume 2 (possibly RCA 120; I don't have the books here) that I tentatively attribute to perhaps Abraham Berlin just based on lock panels. It has the thumbnail buttplate extension, and really early styling to the buttstock and cheekpiece treatment. it's presented as is. I'd disregard the guard completely.
Just some places to start; see what inspires you. The important thing is to have no feature that could not have been present in the 1750's, so get an early barrel profile, an early enough lock, and early enough Germanic furniture, no matter what stylistic characteristics you prefer.