Too cold and windy outside to do compression test.
I thoroughly cleaned distributor cap, rotor and cleaned all the distributor contacts.
I replaced the copper rotor pickup (from another distributor) as mine was worn very short arcing to the rotor.
I ran a new ground wire to the coil, back to the battery.
I had another old set of spark plug wires, from a V8, which I ?made? to fit my V6 plugs.
This made the increased the idle vacuum to steady 17 in hg in Park (1100 rpm), and steady 10 in hg in Drive/Reverse (600 rpm).
The engine easily goes to 4000 in park, with less hesitation than before.
Throttle response seems crisper with the timing at 19 BTDC.
The car is now at least drivable, drove it round the driveway. There is a definite misfire in gear, that?s not there in Park.
It still needs work, but my troubleshooting leads me to think the problem is ignition related. (Swapping carburettors has little effect). I now think I'm losing spark under load.