Coupler height was set by the Safety Appliance Act (effective in the 1910s?), enforced by the ICC, now FRA. Of course, it did not apply to most indstrials.
Standard gauge = 34.5 inches above top of rail to center of coupler
36 inch gauge = 26"
24 inch gauge = 17.5"
These are the maximum, minimum is 3" less.
Reference: 49CFR231.31 Drawbars for freight cars; standard height. Section 231 also has the current regulations for location of grabirons, see previous ICC regulations for eaarlier era.