250-114 in the 75 code says "Where more than one grounding conductor of a branch circuit enters a box, all such conductors shall be in good electrical contact with each other and the arrangement shall be such that the disconnection or removal of a receptacle, fixture or other device fed from the box will not interfere with or interrupt the grounding continuity".
That seems to make the common practice of simply twisting a few inches together, leaving a single stinger for the receptacle, legal at that time.
