Agree -
No, you don't need a deep crescent just because the drop at the heel is more extreme on rifle "a" compared to "b".
The butt plate is tied to the original you are trying to emulate and with a maker like Leman you have a wide expanse of choices - his style changed over the years and from model to model.
Yes, Walnut (Black, North American in this case) is very strong. Perhaps not as pretty as European, but on a stock should easily outlive you.
And in the relative scheme of things, a 50 cal can barely be classed as a "large bore".
One final note on that - there was Walnut stocked Hawken rifles, so it's viable and correct if that's the style you ultimately pick.
A further suggestion here. Take some more time to decide unless you plan on another rifle in short order. Then pick one and don't look back.
When I started, my first build was a half-stock Hawken. I just had to have one. I worked from a "board" so after getting the blank cut out there was enough wood left for a second blank so I cut out a full stock blank that would accommodate a 36" barrel (no sense wasting the wood).
The more I worked on the Hawken, the more I glanced at that full stock blank.
Long story short, I shot the full stock Ohio (that came from my leftover "Hawken" board) for fully two years before I even finished the Hawken - which was sold within months of completion.
Most think of Vincent's when you say "Ohio". Their butt plates redefine "crescent". But there were dozens of Ohio makers. I just chose a style that better suited me.
Maybe make a list, without considering style, of what you want/like/have to have.
It may be something like:
relatively flat butt plate
iron furniture
32" straight barrel in 50 cal
little drop in the comb line
3 1/2" drop at the heel
etc
That may lead you to a style you have never considered.
And if Track doesn't have what you are after, try Knob Mountain (recently mentioned). Most of Dave's stocks are patterned after original rifles, and he has "lots" of patterns.
You can check them out here
(Knob Mountain Stocks)