Hello
Might be worth checking the HT leads.
Beauty of such an engined 4/4 is that it shouldn't take long to find culprit.
I recently fitted a period electronic ignition on my newly acquired '74 and its an unused Sparkrite 2000 acquired at Beaulieu auto-jumble last Sept. Although some may consider it's keeping the points as a trigger to be a disadvantage, I like the changeover switch that allows me to go back to standard ignition and rule out the box quickly.
Good hunting…
Cheers
