i had the same problem the car would misfire occasionally at 70mph and would cut out sometimes after an hours driving sometimes 10 minutes... wouldnt start up for around 20 minutes and tehn would be ok for another 10...
was an absolute nightmare
i changed the metering head, fuel filter, coil, ht leads, dizzy cap, dizzy, fair few other bits as well only to find out that the hall sender was buggered. swapped in for a new dizzy and the car fired up and has been brill ever since...
there is a slight hesitation in the car, driving along at 2-3k rpm, very slight and just feels like its juddering ever so slightly and sometimes the car takes a couple of cranks to turn over but could be due to the timing is slightly out (as it was done by ear) getting it properly done with a strobe and marking all the points so i can do it by hand proprerly next time
Cheers
Saf