Seems the same coil was used on the SD1 V8 which should open up more opportunities for finding equivalents. And I'm pretty sure I've seen coils advertised by some outfit on the back of the Jaguar club mag for about 16 quid.
The coil is just a long bit of wire, the other end is fed with 12v, so you would see 12v on the negative side assuming (if it has them) the points are open and you are measuring between the neg side and earth.
