TexasCheesehead - You appear to have a real Spaulding made belt for the .30-40 cartridge. Spaulding was one of the alternative contractors, supplying belts during the SAW, when Mills-Orndorf could not meet the wartime demand.
Spaulding belts were lighter, leather tipped, and had sewn-on loops, rather than the (patented/proprietary) woven loops of the Mills Company product. IIRC - Spaulding belts used 45, instead of 50, loops.
I think you are correct that your Stamped Brass "U.S." Buckle is a reproduction. The font style and letter lay-out of the manufacturer's name is not original.
FWIW - Lots of photos of troops "in the field", during the SAW, show them using the simple wire "C" closure as a buckle. (Less of a target than the shiny brass plate).
'RCS' - Your .45-70 belt and cast "U.S." buckle look correct to me, especially with the white paint "35" stencil. Your cartridge-loops appear to be woven into the belt and not sewn-on. I don't know why the belt ends are 'raw' (unfinished), but, I have seen it on original belts, before.