It took a while to get the new dizzy and get it in but it's in now and the old beast is running again.
The problem turned out to be a broken wire inside the HEI distributor. My research indicates that this is a common failure point on these distributors. The replacement "Skip White" distributor is a nice unit with a slightly different top cap design and supposedly more power than the stock GM units.
The new dizzy went in fairly easily but when I went to put the top cap on I realized that there was no way it was going to fit. It's just too tall and bangs into the firewall. This is a HUGE problem because the top cap is secured by 4 screws that also secure the coil and the coil ground. On the stock cap the coil is held down by 4 separate screws and then the top cap has it's own 2 screws so it can run without the top cap. Not so with the Skip White.
I trimmed an inch or so off one side of the cap and got it to fit but it was still very hard to tighten the screws because of the curve of the firewall. In the end I just reused the stock coil mounting screws and top cap with the new distributor. All the screw holes and mounts in the aftermarket cap were the same as the GM unit.
The old cap and rotor looked pretty rough and they had 20K+ on them so it was time for a change. The truck revs a lot smoother now but I'm getting a little bit of detonation at full throttle so I'll need to back the timing off a bit and then maybe this summer I'll play with some springs and plug gap.
The point of failure:
Skip White rebuild kit:
Skip White top cap:
GM top cap:
Skip White complete distributor:
