RD - you can rotate the camring and not have anything out of kilter - you just need to reverse the HT leads as well.
The rear cylinder on an engine whose crank turns clockwise from the timing side will be the one fired after the shorter period of 'points closed', the front one after the longer interval (as that's the one that is running 'late' at the mag). The firing interval is 150:210°, or should be if the camring is a 60° one.
Manual control on a 60° V engine means the mag has to be in super good shape. In the advanced position the second cylinder is already running 30° retarded from the ideal firing point, and with additional retard applied, that second spark will become appreciably weaker still. (You can't compromise the setting by asking one cylinder to fire 'early' because it won't, as the HT coil won't be charged up. But you DO want to get that first spark to arrive as early as possible, ie with the camring as 'advanced' as you can safely get it in its housing; that way the delay on the second lobe is minimised.
Couple of supplementary things:
Traditionally, the second, weaker spark on a V is arranged to be the negative one (spark goes from centre electrode to earth on plug), so reversal of the magnetism is a good move if possible. (Doesn't make THAT much odds, but every little helps.)
Also it's very worth checking the HT brushes' position on the brass strip of the slipring at full advance and full retard on both cylinders with the points just opening- to be quite sure the brush is always fully on the strip at the firing points. The typical slipring on a KVF is stretched, with manual advance/retard, on a 50° application, so this isn't a trivial point. I haven't tried a KVF at 60°, but I can say that a manual mag from an HRD needed every millimeter of the brass strip on the ring to cover the range. It might just be that a reduction in camring movement to limit retard would be necessary, because if the spark flew partly across plastic or bakelite, trouble wouldn't be far away!
Have to say, my heart sits in my mouth when testing wide-angle V-twin mags, as the requirement to get that second spark at reasonable rpm is pretty important for easy starting. On a 50° V, the difference in rpm required to promote the 1st and 2nd spark would typically be about 30 or 40 rpm, with the first spark (5.5mm Lucas-spec test gap) delivered (100% continuously) at under 130 rpm (at best). That's 260 crank rpm rising to 320-340, say. Doesn't sound a huge lot - but in kickstart terms . . .