L.A.B., Those studs I am refering to are indeed the lower clamp pinch studs. On the earlier Nortons including Commandos they screw in from the rear and the forks are tightened by a nut (5/16") that goes on them also from the rear. The S type and early Roadster have a stepped stud with a 1/4" dia threaded protrusion that stands proud at the front of the clamp onto which the headlight ring bracket mounts. The clamp itself is still tightened by the 5/16" nuts on the rear. The clamp I have has the S type studs fitted and this is why I assumed it was an S type lower clamp. My confusion is caused by the fact that there seems to be no provision for this lower clamp to but against the frame stops on the steering head on full lock. I do note from a glance at Bacon's book 'Norton Twins Restoration' (page 142) that the earliest frame illustrated here has a plate below the tank/coil mount that would act as a steering stop for the clamp that I have, but the slightly newer frame pictured above has the two lugs welded at the bottom of the steering head equidistant from an imagined centre line. This is the frame that I have and I need to know how the steering stops work with the lower clamp. It may well be that I have an earlier clamp, in which case I may have to either modify this with the fitting of some kind of peg, but I am confused about the studs which are definitely from the later model.
As you well know I am technically inept in the computer department so you might have to pop over with your digital camera and help me out yet again! I may have to wait until my next trip abroad to have a look at a similar model unless some kind soul has a bike of the right age and a digital camera.