I would think if you test the complete ignition system; distributor, coil, box, all together on the distributor machine as it will be run in the car you’ve basically covered all the necessary bases and eliminated the important variables. If a guy can’t put a clean 12v signal to his ignition he should be playing with LEGO’s.
Really, we are just playing with expensive Legos. I should put the distributor in the machine that I just tested on the dyno and see if it has the same amount of retard. It should. Not enough hours in the day.