I agree with Pete. Looks like a Weaver flatcar to me. Definitely look like Weaver die-cast trucks and couplers. The half-round uncoupling disc on the coupler shank gives them away.
I like the look of the wire grab irons that you added...definitely improves the appearance! You should consider slicing off those thick stirrup steps and replace them with scale-sized metal or even plastic ones to further improve the look.
Please post photos of your finished pulpwood car!