For some reason, no one seems to be reproducing the taller buttplates with longer heels that you see on some iron mounted Appalachian guns, like the Bogle rifle or other early guns (when I say early here I mean ca: 1790s-1810-ish). Most of the ones out there seem to have the long toe extension out back, i.e. the heel of the buttplate sits well forward of the toe.
Some of the Hawken or other plains rifle style plate profiles could work - as long as the comb extension is long enough (some of the ones offered are too short.) However, they are generally too narrow for the really early mountain rifles (I think the Bogle buttplate is around 1 5/8 or thereabouts). Susie at MBS offers investment cast late Sheets Virginia buttplate and also a Peter Berry in steel that might be better choices - either could be modified.
If you do use a Hawken I would modify it as you said by sharpening the inside corner where the heel meets the buttpiece. Also some of the Hawken plates look like you might need to narrow the toe a tad. But that will allow you to reshape the sides a little too, and before you know it, you can't tell it started as a Hawken...
Some iron mounted guns have the upper and lower parts of the comb extension parallel, while others have an upward slant to the lower edge - this feature lends itself to a nice look with a "soft comb" - i.e. the comb is more or less straight, but just the front part of the comb has a subtle radius that begins a little back from the nose and gradually steepens - you see this on SW Virginia guns a lot.
Guy
