Well,If you're going for a H. House "woodbury" style, on the big ones the blade's back (top) is about 1/4" thick right where it emerges from the cast bolster, and is constricted (looking at the blade from the top, it's concave on each side for the 1st 1 1/2"s or so, and tapers to only about 1/8" thick at about 2-3" from the bolster, and keeps thinning all the way to the tip. The cross section of the blade for the whole length is triangular, not a flat slab of metal with beveled edges.
But of course this type, as far as I can find out, seems to be a total fantasy for 18th century.