I don't know much about the pre-74 bikes so my apologies for my inexperience, but I do know that the green frame that is most sought after is a 74, not earlier. This is because Paul Smart won the Imola 200 in 74 - which is one of the reasons why I have ordered the Paul Smart 1000 replica which is a tribute to the man and that win.
IMO anything earlier is not worth anywhere near as much money.
Another fact that I am not sure about - please verify independantly, is that I believe they weren't called SS's back then ... they were an S. The greenframe is a 750S and my understanding was that SS's came out after. I would be thinking that you are looking at a GT.
I am however, not the most knowledgable person and I'm sure there are many more knowing more than me. In fact, I would try and speak to some one in the bevel owners club to gain more of an understanding before making any decision based on my information, the 5 pints of XXXX (yes you can get it here!!) and the two glasses of Brown Brothers Tarrango I've had.
If you find a genuine 750S greenframe built in 74 and you can't buy it for whatever reason - ring my number immediately - whatever time of day I don't care and let me know. I will do my best to own it very quickly!!!!!
Have a nice evening
