Does anyone have copies of Bus & truck Magazine (70's)?

Hi guys,

I'm trying to find out the history behind the letter used (A + B) for A-trains & B-train. Do the letters actually stand anything? I already know it refers to the coupling type (i.e Draw bar or fifth wheel) but I want t know why letters are used. Do the letter stand for anything? I've heard people say the B stands for Bogie or Bridge. I want to get the the bottom of it and find out if this is true or not. Who coined the letters, who coined the terms A-trains and B-trains. Im hoping ill find my answer in this old magazine somewhere between 1972-1979.

Example of one of the magazines cover page attached.

EDIT: I should point out that I am not from Canada (I am from Australia), so I am not able to visit libraries in Canada to find some copies.

Cameron