Yeah, that's not a typical SC II. I've never seen one with the forged dropouts, only in a couple of pictures. We have a couple of 75 frames and a 74 and none has the forged dropouts. Also, never seen one with the Jubilee RD nor the Stronglight crank with the Ben Hur guard. The crank is what you will see on GS bikes of the era. Two of ours had steel Nervar Sport cranks and the other an alloy Nervar Star. That Stronglight is a bonus.
The headset appears to be one of the proprietary 26 tpi headsets so the steerer is threaded 26 tpi to match. Just like all three of ours. 27.0 mm crown race machining. Those headsets are pretty unique, you'll discover when you open it up. the races are not angled, the balls sit pretty much straight up and down. Fortunately, they are pretty durable headsets but used parts are available, if needed, as that hs was used on everything from the Sports up through the Super Course. There are a lot of them out there.