...this is from a blueprint produced for Bob Gurr way back in the in the planning stages. According to Bob, many concepts were tried for the look and feel of the cars...
It's an interesting California type car, which reminds me of early Pacific Electric interurbans. As for the cars that eventually were made: as you say, they were standard double-platform city-type horsecars. They would've also looked right as first generation trolleys or, for that matter, cable dummies. It makes me wonder if WDW might have been entertaining the idea of running steam trains, trolleys, and horsecars on the FWRR.