I have long suggested that one possible fix for the Marelli distributor issues and threat of resulting fires might be to somehow fit two 6-cyl distributors. Just connect each Marelli ignition coil to its own distributor cap, and route the wires from each cap to one bank. The Marelli would continue to handle timing and spark issues, so the 6-cyl distributors could be gutted, the only parts needed are cap and rotor. Choose the right distributors and the caps and rotors could be very cheap.
I just recently discovered that both MSD and Jesel make belt-driven distributors designed to be driven straight off the camshaft. Here’s the Jesel version:
As far as I can tell, these are only offered for V8’s. Still, it offers ideas for how 6-cyl distributors might be fitted to the Jaguar V12. Might even get away with just one, using the original Marelli distributor for the B bank (that side rarely fails). Of course, the Marelli distributor would look silly with every other plug wire hole unoccupied.
Anyhow, at least four ideas come to my mind right off. First idea is two 6-cyl distributors in the vee, one driven directly from the original distributor drive gear and the other driven from the first by one of these cute little drive belts.
Second idea would be to mount the 6-cyl distributors horizontally near the front end of the cam covers, and mount a stub shaft off the front of the cam sprockets and out through a hole made in the covers (with an oil seal) to a drive belt to the distributor.
Third is to forget the drive belt and simply mount the 6-cyl distributors directly to the front of the cam covers.
Fourth idea is to drive both distributors directly from the crank. That would require a 1:2 ratio in drive:driven pulleys and either two sets stacked or one loooong belt with an idler or two.
All these ideas would definitely involve some machining work.