In my opinion get rid of it unless you have some kind of antique trailer with hydraulic brakes that would require it. All those were a crude design, little ability to modulate trailer braking effort for varied load requirements. They were nearly as bad as the ones that had the surge brake controller built into the hitch. I bet that was already way outdated when it was installed on a 1969 model.
Disconnect line from that goes into the master cyl and replace with a brass plug. Actually the old master might have an adapter installed that can just be removed.
Heres some links for more on hyd brakes on trailers
http://www.dogpile.com/dogpile_prefe...7?_IceUrl=true