I would think that the transformer coil would be the difficult component to replace. Mainly due to its small size; its electrical characteristics aren't too unusual.
It may be possible to get a transformer coil rewound by a magneto repair specialist, but I wouldn't expect that to be cheap. There are only a few of these specialists about, and some also rewind other very small coils, such as the pulse generator and trigger units used in more modern motorcycle ignitions.
As grumpy says, the capacitors of that era were very failure-prone, but it's easy to find a far superior modern equivalent. Same for the rectifier diode, and I'm a bit suspicious about the reliability of the original type. If it is indeed a selenium type [as stated in that 'The Motor Cycle' article earlier in this thread], those weren't known for their durability.
I would be very surprised if that cutout switch is a bimetallic strip - plain hard brass would be much more likely.
