We have had a fruitful evening.
Many thanks to all with your suggestion. Now I know the 260 has a clean fuel line, and properly grounded, with fine sensors.
When the injectors were inspected, it was all clean as it should be. No blockage or damaged ends.
That was when it was decided that the timing be checked.
The distributor cap, when opened, was somewhat eaten away by age. So, we suspected that could have been a cause.
Now, we are waiting for the part to arrive and will put it on tomorrow morning. Hopefully, this solves the entire thread.
BTW - I have offered the techs a shout of beer at the local tavern tomorrow evening for having spent many golden hours pouring over this matter .... and of course, you are all invited too (in spirit, if you're too far away) ...
More updates tomorrow ...