After is warms and if let to sit at idle does it finally die? My 722 w/ same 1.6 Ford did this. I tested, troubleshooted, replaced points/condenser/rotor/cap, and tried nearly everything. Finally was going to send the distributor in for a full look-see, cleaning, and fix whatever was found to be a problem. When the distributor shop found out it was a Bosch out of a 1.6 Ford industrial they told me to save my money and their time. They wouldn't even look at it.
Their story was Ford cheaped out on the specs to Bosch and didn't pay the extra $ to have the distributor shaft case hardened. So through time and hours the shafts see wear. Not so much a problem when the engine low hours and when higher hours units are cold but as the block heats and expands the bore increases allowing the shaft to wobble a wee bit. That makes it nearly impossible for the point gap to remain stable.
Sounded a bit like a theory to me but I did this. Bought a brand new Pertronix electronic ignition distributor. I mean the whole distributor and not just an EI module for the existing distributor. All I can say is that by doing this all of my problems were solved.