Convert Proform ignition to Pertronix?

Thanks 67Dart for the clarification on resistance increasing, and Bewey for the advice. On the CV8 the ballast is shorted by a relay that comes off the ignition switch, and this works fine. With the old distributor in, all the voltages are correct. There's a small drop (just a volt or so) on cranking over the battery itself, and 11-12v at the coil primary. Really good spark.
With the proform in, there's only 8v coming out of the unit, and no spark. It had previously run OK (in fact perfectly through the whole rev range) for a couple of hours with the proform. I know this sounds like a bad earth, or a dry joint, but I have tried direct-wiring it from the battery, the same.
I saw a web page on how to test the ECU out of the car, I think I will try that. Disappointed to hear the pertronix has problems, I thought they were the bees knees.

Re the CV8, the Mk1 had a burr walnut dash, and a 361 engine (5.9 litre). For the Mk2, they put in a Formica (!) dash - at the time this was the latest hi-tech material (and a 383). They soon realised the Formica looked awful, and reverted to walnut for the Mk3.

The CV8 (mine anyway) has serious heat soak problems, causing poor/no hot starting from no spark and/or fuel percolation, and sorting the ignition has been just one step in overcoming this. Incremental improvements have been a new edelbrock carb, a 3/8 heat gasket under it, Carter electric fuel pump, new coil & ballast, moving the coil to a cool place, replacing the high current earth strap, each of which made it a little better. It's frustrating that the problem is now cold starting (with the ecu)!