The initial problem was something akin to a misfire on a cold / damp morning during the days of (old) Kettering ignition systems when the distributor cap got some moisture in it. More noticeable when going up a slight incline - slight increase in engine load.
The misfire would apparently disappear when things had warmed up a little.
The problem worsened to the point that a diagnostic tool reported a coil malfunction.
Replaced coil - problem solved. Or was it?
Similar issues arose and further diagnostics reported other coil failures.
Bight the bullet and replace ALL the coils, AND the spark-plugs, because they're not the easiest things to gain access to.
Having heard reports of plenum chamber gaskets also being a problem, I replaced those as well, while access was easy.
Now, I have what seems to be a complete ignition failure of one bank of cylinders.
Any suggestions??
I'm wondering if this might be an electrical / wiring issue because of the "disturbance" to the loom when accessing the rear cylinder bank, which is an absolute PITA!

 

Welcome to the forum