I recommend getting one of these.
IIRC it was $5 at O'Reiley's.
Makes cheeking a HELL of a lot easier.
Plug wire positively snaps on, and I use the shock tower as a ground.
Distributor wire will slide on loose, but weight will usually allow a good contact to check the coil as well.
I like this style MUCH better than the style with a light bulb.
I'm going through the same issue on my latest /6 parts car.
Something in the points distributor was wacked, despite it passing every test I did.
Wasn't telling coil to fire.
I just got a JY electronic dist, and wired that up.
Now the coil is firing, and after replacing a third cap, at least one plug is firing.
It's fighting me every step of the way, but I'm making progress.