Jason,
For this period, I would guess the link & pin coupler butt would have backed up to the end of the draft gear and a 1 3/4" rod with a 2 1/2" square head set in a socket in the back of the coupler pocket, would have ran through the hollow coupler shank and the draft gear and a nut and keeper key would have been on the back side of the draft gear. That is based on the way that Billmeyer & Small was building freight draft gear and couplers in the 1870s/80s. Since the Great Western Manufacturing was new to the car building business, they probably copied ideas from other manufacturers.
Dave