Hi Richard,
You don't want several degrees of float on the camring, for sure. It might be possible to eradicate it by shifting the pin's position a bit . . . to do that, prise the little cap off the top of the pin (it'll come without damage, v fine chisel or screwdriver), to expose the slotted head of a threaded item with an eccentric on the inner end. The eccentric is there to give fine tuning of the camring position, and will have been set to the best position for best sparks at the factory. However, chatter over the years might have worn it a bit. Because it's eccentric, you should be able to turn it a little to get the eccentric bit to fill the notch a bit better without moving the camring more than a gnat's whisker (which will be OK).
Quite often, I've made new eccentric-ended screws to eliminate this hassle.
The pin in the outer end acts as a locking device, as you'll see, by expanding the slotted outer end of the thing so it doesn't move. However, a short bit of threaded with a little locknut works just as well, and in fact you could make a bit with a file to engage exactly with the notch in the camring. Then screw it in and refit the camring. Thread is BSF, 5/16 from memory.
Also, would suggest you make up a gasket or seal thick enough for the end cover of the cb housing to pinch against the camring, to stop it fretting if it's so inclined. Often, the seals supplied or fitted don't actually engage the camring at all.
If the camring is a very loose fit in the end housing, then it might be worth using a dab of loctite on a fixed mag. The risk with loose-fitting camrings is that the firing interval between cylinders can be upset by several degrees if the ring is off centre (quite apart from there being a noticeable difference between the points gaps on the lower and upper lobe of the cam). Perfectly equal gaps are less important than 180:180 firing interval (as long as the smaller one is c. 12 thou) - but the firing interval is hard to measure. A static test can be done with a rotary table and a buzzer of the Brewington sort, but proper dynamic testing requires more serious kit with rotary spark gaps and a protractor to see what happens up the rev range, when things can look rather different from at rest
In this regard, it is also worth looking closely at the pivot for your moving cb point. Wobble on there has some of the same effects. If very worn, the pivot post can be replaced (fiddly); if not too bad, a new set of points might help.
Hope that helps a bit. Not sure that any of this will bring the sparks back however, unless there is a short on the LT side for one or other reason. My mate KenF might chip in if I've missed anything . . . Cheers, Bill
Just seen Dutch's . . . only early mags have the axial screws for limit stop operation - they don't have the eccentric bit. Suspect you have the later sort Richard?