Alrighty then. When I built my rifle, I used the dimensions that were provided by Mr. Shumway, and by carefully measuring in the photographs the items whose size I knew, I was able to come up with a ratio that applied to all other parts of that photograph. And so it went until I have enough to make a profile drawing of the rifle. Here are some of the information I recorded right in my book.
Known from the text: overall length: 63 1/2", barrel length 47 1/2" and .61 cal smoothbore. That's it. That's all that was provided.
Now other's extrapolation may not be the same as mine, but here's mine now, and it's what I used to build the rifle.
Width of butt plate at it's widest excluding the raised patchbox lid: 1.875"
Height of the butt plate, measured from the toe to the line of the comb at the heel: 4.959"
Width of wrist of the stock at its minimum: 1.30"
Height of the wrist of the stock at its minimum: directly behind the spur of the trigger guard, and through the fleur de lis beavertails behin the tail of the lock plate - 1.27"
Height of wrist from the step up through the silver wrist inlay: 1.64"
Patch box: diameter of hinge at the knuckles: .02065", width at the butt plate: 2.067", width at the hinge: 1/908", AOL patchbox: 7.1095", length of head from fore side of hinge: 2.703", width of the dome at the butt: 1/118", length of lid to the knuckle: 4.25", width of fleur de lis across the tip: 1.357", width of fleur de lis at the middle: 1.741"
Lock plate : 5.32"
Length of trigger guard bow from back of spur to front of boss: 2.55"
Forward most ramrod pipe: 1.6"
Length of nose piece and flame inlay: 2.353" Flame length: 1.053"
First barrel pin from the muzzle: 2.8"
You really must get yourself a copy of RCA Vol. 1 (to start) Without the actual rifle in your hands, it is the next best thing, and i don't see how you will come even close without it. Also remember that the rifle you posted is not No 57 RCA Herman Rupp 1793, but it's sister.
Good luck.