My first southern mountain styled rifle, built from a kit, did not have cast off. I've since incorporated a little cast off into the last two North Carolina inspired rifles. The first was from the piedmont region (Deep River, if I recall). The second is Appalachian. I find they fit me better.
Cast off may not be historically correct for a properly designed rifle from eastern TN or western NC but I adjust a bit to fit my size and geometry. I'm tall and broad shouldered with a long neck. 1/4" to 3/8" cast off makes it easier for me to align the sights without craning my neck over.
Alternatively, I guess I could have increased drop at the heel and comb even more...
How one achieves a steady hold when shooting also makes a difference. For me, butt is fit into the crook of my shoulder joint, just on the upper arm. Rifle is held generally across my body. Right elbow up, about horizontal. Left elbow tucked in against my chest. The slight cast off brings the sights closer to my natural eye line.
I'm by no means suggesting every rifle should have cast off! I'm saying if you are building for you, build what fits you.
You might make a "try stock" out of a couple pieces of plywood to play around and see what fits you.