You are correct, Brian. I just finished Mallory Hope Farrel's book "SP Narrow Gauge". He claims the cars were arranged in pairs for a while with a 3/4 coupler at each end of the pair. The other couplers were changed as time permitted. By the way, the above mentioned book is a dandy. I paicked up a used copy from a Dalles book dealer but I would certainly recommend it to anyone interested in NG. Someone earlier in this thread mention Bibliofind.com. I have had great success with them for what it's worth.
Les Clark