OTL A7V had no sponsons, A7VU prototype did but carrying cannon and at the rear
US design was something that turned out rather like the A7V, but was deployed months if not a year before the OTL Germans formed a committee to start investigating tanks. US design would likely be similar, as the Holt tractor used as a base is a US design, which would make sense for US to built off of. Of course some detail differences would creep in. Incidentally cortz#9 must have modified the design, because that is not the one in my folder as my Mk. 1 Barrel had no sponsons
For GWI light barrel, something like the Ford 3 ton was my old guess
^^^ --- This thing, right? Well! I can understand why you said it was your old guess, if not your current one still. Fairly interesting design! An issue with it though is that, I think, its based off the FT-series of tanks, which would make it based off French designs. I think and argument can be made however that the US would try to make a light-tank series inspired by the FT --- perhaps they captured imported models on the frontline while fighting Confederates equipped with French-imported FT tanks, reverse engineered the design, and made something like the 3-Ton. Its not a bad idea though. Hell, I bet Custer would absolutely love the idea of a smaller, faster barrel.