It is the SH-100s headshell, but incomplete: it misses the plastic to part for readout of the overhang scale.
Actually it is not as rare as you seem to think as there were many, many SL-1300-1310-1400-1410-1500-1510MK2 turntables made in the '77 to '79 period.
Since it is incomplete and not that rare, don't get your hopes up high for selling it for a lot of money on ebay.
Just keep it and use it, if you like it. I think it is a bit on the heavy side with 9+ grams. The newer Technics headshells were 7+ grams, which is better for most arms and cartridges.
PS Nice place Graft, I grew up in the adjecent De Rijp!