It's a model 1014. The field one without the interchangeable cords was the 1013. The two little lugs were used to attach the leads to a 310-type plug. I can send you a plug that will work on it.

The orange test sets were the last of the four colors to emerge. The first ones were dark blue, then a lighter blue, for field work. The yellow ones were for CO/PBX work, and generally had the plug/connector as yours does. Then the last ones were orange for either application.

The real early ones had two distinguishing features: A TALK/MONITOR switch that was concave, instead of convex. It was almost impossible to operate with a gloved hand. The other feature was a thumb warmer in the guise of a large wire-wound resistor in the talk circuit that would overheat and melt the plastic switch handle.

Back in the wacky 1970's when they were first introduced, guys would take two sets and marry dissimilar colored halves to make a psychedelic version.

Arthur P. Bloom
"30 years of faithful service...15 years on hold"