I owned 4 of these cars during my mis-spent youth. All were lovely but had the dispicable Lucas electric system, where no manufactured piece was ever rejected for being substandard. A mechanic buddy from Des Moines (more mechanical than me) uncovered a Delco of England cross reference manual. Turns out a Pontiac voltage regulator and (with minor modification) a Cadillac Delcotron alternator worked perfectly. Mallory made a replacement distributor that was a drop in. The starting/charging problems with my Jaguar were resolved.
The best fix I’ve found for a Jaguar was to drop a GM V8 into it. Tends to cure those overheating problems too.