It looks quite 'well-used' as they say, but as long as the camring isn't a sloppy fit it ought to serve.
You can sleeve the enlarged hole - probably bodged to allow the use of a larger screw than original into the thread on the body on that corner . . . they can strip. The housing should register OK on the other holes though - so not a huge prob for fitting it.
The missing pin is a 1/4BSF screw with an eccentric tit on its nose - and it has a hole in its head for a small pin to be tapped in when it's set in position to lock it there.
What it does is offer fine adjustment of the camring position, to get the ring in the optimal position at full advance of the instrument.
Any 1/4 BSF screw with the nose filed to about half diameter, and a slim locknut on the outside to lock it, will work fine - or you will need to fiddle about with a drill and make a pin to replicate the original.
When setting the camring, you want the points to just start to open a few degrees after the flip point of the armature, with the plunger at full advance (in this case, fully 'down' the 'ole as it's for 'slack advance' on an anti-clockwise drive magneto).
It is very important that the points don't start to open before the flip point (or right on it for that matter) because the mag is not ready to discharge until it passes the flip point.
If the camring is set far too far advanced, there'll be no sparks; if it's a bit too advanced the mag will spark at low revs but you'll lose the sparks as revs rise as the lines of magnetic flux 'bend' with speed. Usually, with the eccentric tit set at about mid-point, things will work quite well, but the newness of the heel on the contact breaker and wear on the camring influence when the points actually start to open. It is worth playing to get what seems to be the best low speed spark at full advance, by spinning the mag by hand on the bench, and then checking that the sparks don't disappear when you spin it under power. If you can measure the speed of rotation, you ought to get all sparks, across large gaps (grind the earth electrodes off a couple of old spark plugs to obtain 4mm+) from somewhere not very far north of 100rpm. Lucas said '90% of sparks across 5.5mm test gaps with three sharpened points at 130rpm' for the K2F.
The eccentric can go in on the top or the bottom if there are two threaded holes to choose from, as the camring is symmetrical. But you need to choose which before grinding a notch for the cable plunger on one side, and enlarging the slot that allows the advance/retard.
As a point of note, the large slot for the AR movement in a manual camring is usually about 10.5mm/11mm from side to side, which would give you about 20° movement on the magneto, or 40° on the crankshaft. Less is plenty though - and the worst thing to do would be to make it too wide - because then the plunger might disengage from its notch at full stretch one way or t'other and the operating mechanism jam in the housing. On my own machines I usually restrict the movement to a bit less than standard, as we don't really need massive amounts of retard IMHO.
