You might want to spend a bit of time, effort and gasoline to actually see and handle a Soddy rifle. There is only so much that you can get out of someone else's photo (Ancient One, don't have a clue what "rca"means except it brings to mind a dog listening to . . .)
Some time in the last century I was fortunate enough to spend time in Pennsylvania, to photograph and handle a number of rifles. Can't say that my 6 or 8 guns were anything to brag about, but they were a lot better than the Martin Shell I made strictly based on Joe Kindig, Jr.'s book.
As an ex-pat Pennsylvanian I don't know Soddy from anything else in Tennessee, though I am impressed by that Dave Byrd book Gunmakers of Buffalo Valley & Greasy Cove And Jerry Noble's books. Noticed in the one Tennessee rifle I had, and one Virginia rifle I still have, that the set triggers were offset from the centerline in the plate, toward the right side/toward shooter's hand. Dunno if anyone sells such triggers these days, would be a nice touch.
Never used a precarve, myself. At one time owned 5/6 of a Michigan maple tree, the last 1/6 went to Larry Mrock. Need (!!!) a new flint, looking over a blank I sawed out in the '70's, machine inlet for 7/8" bbl. Have a Chambers brass plate Siler, GM .50 x 7/8" bbl, assorted buttplates & triggerguards. Probably can remember how to drill the rr hole, less confidant about making a domed patchbox lid for Shroyer style rifle. We'll see.