I am just throwing this out there cause it sounds good and I know more knowledgible people will have the right or closer to right answer than me but I am saying maybe valve train? cam? lifters? pushrods? Thats me sense you gone throught the fuel/air and spark part I can only think mechanical.

 

have you checked the resistance in the wires where the cylinders went bad?

 

the "all of a sudden" part makes me think that something broke [maybe in the distrib. or even a crack in the intake manifold] I dont think the cam got wiped out cause thats not an "all of a sudden" type thing. THe reason im thinking crack in the manifold is because if a crack occurred in the dual plane manifold in the right place it would disturb cylinders on both sides of the engine [cause of the design of the dual plane intake]. Another thing could be the bushing in the dizzy coming apart and its arcing out or not able to produce a signal. Do you know if the cylinders in question are in a sequence that corresponds to the firing order? {eg: 6-5-7} Just some thoughts, hope they might help or give you something to ponder. Good luck and make sure to get back here and; WELCOME TO THE FORUM!!!

 

You solve this issue yet?

I assume you checked the basics fluid wise, always a good place to start.

Any of the rods bend, slight stretch, but possible solution.

 

What was the compression of the all the cylinders? Have you installed a spark tester to make sure that you were getting spark?

 

How's your timing relative to TDC, Is it possible you may have a stretched timing chain and skipped some teeth ?