I had the vibes in my car shuddered the whole car but only in fifth gear at 50 mph!!
Cured it but took some head scratching, done all the usual, was DIZZI in the end, the bush had seized to the shaft in the top of the dizzy, and had spun in the housing, the phase gap ranged from ZERO to 2.9mm, and yes it still ran almost perfect, just a misfire when hot below 1500 and very light load.
Fixed dizzy with NEW BUSH(bronze), machined shaft for £35 all in.
Just a thought might be worth a look as only a few minutes ?
tabetha