In designing your rifle, with respect to architecture that does not slap your cheek bone, consider the drop at the comb to be the most critical dimension. For the rifle pictured here, my Jacob Kuntz compilation piece, these are the critical dimensions:
lop...13 7/8"
drop at comb...1.583"
drop at heel...3.550"
measurements taken from the top of the barrel flat
height of rear sight above the plane of the bbl... .219"
" front " ... .157"
barrel (Rice) 44" x .40 cal B weight swamped
weight of rifle 8 1/2 pounds
Comments: the buttstock shape does not have to have an exaggerated drop at the HEEL to look good and certainly not to shoot well. In fact, many jaeger rifles and English sporting rifles have a virtually parallel to bore comb line, but the drop at the comb keeps your cheek bone in the comfort zone, just as an example.
I second the use of Eric von Auschwege's Lehigh plans. He and Tom Curran were instrumental in designing my rifle pictured here. They took detailed and accurate dimensions from the MET's two Kuntz rifles.
...just looking at your drawing, Mr. t, and I see you have a sizeable rod hole drawn. My .40 cal rifle has a 5/16" hole for a .40 cal. You could go as large as 3/8" for a .54 cal, I suppose, but remember - the larger the hole, that deeper through the lock your rifle will end up. Keep it as slim as you can.