Mr. Sharps: you can make the precarved stock work, but you will likely have to remove a lot of wood to get "there".
Here's my advice: often precarves have an exaggerated step along the lower butt stock line. The originals achieve more of the look by leaving the lower edge of the stock square until it arrives at the back end of the trigger guard, where the apparent step begins. Then the wrist is rounded ahead of that accentuating the appearance of a stepped wrist. The same goes for Jacob Kuntz work.
Second, when the butt stock is finished, it will have a swamp along the sides from the butt plate forward, flaring slightly as one approaches the lock panels. Lay a straight edge along your stock as it is now, and see if there is a swamp in the stock. If not, make it so, No. 1.
Third, the wrist drops down immediately behind the barrel, not at the end of the tang. In fact Rupp filed off some of the back end of the barrel of 1793 to achieve that look. the top line of the wrist is a very gentle curve, terminating at the transition to the comb.
Fourth: the comb line is a gentle arc, much less so than the to line to the trigger.
Fifth, and arguably the most important: your web between the barrel and the rod hole is likely around 3/16" - 1/4". Set the barrel deeper into the wood, leaving only about 1/8" of a web. This of course depends on how much wood you have below the lock and through the wrist vertically. You will likely have to notch the barrel for the forward screw to pass, but that's how you get that ultra skinny rifle through the lock section. The lock gets mounted above centre on the side flat of the barrel.
Sixth: The cheek piece is only about 2 1/2" long along the bottom edge. I have to shorten up the one on the piece I'm working on now, and I've already done it twice. Otherwise, the carving behind the cheek piece gets scrunched.
Seventh: reduce the wood along the barrel, especially at the breech end to way less than half of the side flat.
There's more naturally, and if I'm out of line, I hope others like Eric K., Eric V.,and Allen M will jump on this. I'd love to hear from Mark W. too, if he's still posting here.