Andy,
The Lucas parts book does not have a specific magneto listed for the Spitfire.
However it does list the type for the other A10s.
It would be pretty safe to say that the Spitfire used the same magneto as the Rocket which was, in 1960, 42380A.
This has a screw on end cap, clip on pick ups, the same each side which is the hexagon universal type. Manual advance.
John,
I have to disagree with you whether magnetos from other makes will fit.
Way back when I didn't know about chamfered bodies I fitted a magneto from a Triumph which is the type with the larger square "competition" points housing. I had no clearance problems.
This was on a swinging arm engine. I have never tried fitting other types to a plunger/rigid engine.
Trev.