Interesting one Julian.
Most of the ones with axial screws (usually early K2Fs) have them at about 5 o'clock, and they are disposed to suit a large notch (like in the pic) on the camring, without chatter. The screws are placed where the factory put 'em, with no provision for fine tuning. I'm assuming of course the mag is going to be used with an ATD?
If the internal timing is out, and assuming the points heel and pivot post are good and not causing error due to wear - and the cam lobes are good too - then there are a couple of things you could do. Small adjustment using the self-same position of the camring would probably be difficult because it would require the screws to be set so close to original they'd overlap the 'oles. But you could invert the camring 180° and drill and tap 2 new 'oles up top; or, and is what I'd probably do - is make a small notch in the ring wherever suits best and then drill and tap the housing radially (wherever suits best) for, say, a 5BA screw, to engage in the new notch. There's enough alloy there to hold it, and if it's a fixed ring you could apply a bit of loctite if you were worried.
Or, it looks as if there are 2 notches on that ring? In which case you could drill/tap and use the other one, or a combination, or whatever!
Or, you could make some fatter headed screws, thinner pin-like ones, or eccentric-headed, to adjust the position a bit if you could be bothered.
An interesting thing though is that from the pic the housing seems to be for a manual mag with a bolt employed to lock the camring, so I wonder quite whether it's how it was made, or has been modded somehow.
If you really wanted, you could get a camring housing with the extra meat on it for the eccentric pin, and go that way, but I wouldn't think it was necessary frankly.
