The ignition load is greatest around torque peek.
The spark voltage and resulting current will take the easiest path.
Let's go with a bad wire that is burned through as a simplistic thoretical example (I don't think you want me to get into a physics course here):
These are theoretical numbers for an example, ignoring impedance, transmission line charatoristics, and a host of other things we don't need for this. Your numbers will vary.
At idle, with no load, your spark plug gap is the equivalent of 50 ohms.
You have a burn in your wire, and that gap is the equvalent to 500 ohms.
The spark will ignore the burn in the wire, and the voltage will jump the plug gap - this causes a spark inside of the cylinder and the fuel will ignite.
Now, as your RPM and load increases, that resistance from the plug gap goes up. At torque peek, that 50 ohms may be 1000 Ohms now.
The voltage will now take the 500 ohm jump to the header rather than the plug, so no spark inside the cylinder.
At the higher RPM beyond peek, the the load may drop to 400 ohms, so the plug once again fires.
The main thing to understand is there is a variance in what the plug load is based on RPM and load, it isn't constant, and it isn't straight up.
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If the resitance of the plug is too great, and there is no other path (like you gapped them at .300) it is possible there will not be a spark at all. A specific voltage will jump a specific gap. Beyond the gap it can jump, there will be no spark.
Compression, gap, RPM, and timing all change this plug loading.
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It is also possible that your gap is too small, in that case there is plenty of current, but there isn't enough open air spark to keep the mixture lit. Again, this goes up around torque peek and back down again in higher RPM.
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All this can be trumped by an MSD box that is bad, possible something like the rev limiter is sorta kicking in - did you remove the pill?
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Also a distributor / rotor / cap that is misaligned can cause the same issue. You are looking for something that is marginal, not something that is completely dead or disconnected.
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First thing - check the cap and rotor, make sure no moisture and everything is installed correctly and there isn't any burning.
Next, check the wires. Unseat and reseat. look for burns. Measure the resistance with an ohm meter. With MSD 8.5's, it should be 50-70 ohms a foot. With the other MSD's, 500-600 Ohms a foot. In my opinion, any plug wire over 600 ohms a foot is not on my vehicle. A quick check is to bring your old plug wires with you and swap them out. Many times old plug wires work better than the wires that replaced them.
Then double check the plug gap. Set to .045 as a starting point. Too big, possible the spark is not happening, too small, the mixture isn't staying lit. .045 is a safe gap range with a N/A engine. if you are running boost (though I don't remember you saying you have a blower), then gap them to .030.
Once that is finished, set the timing. Too much timing (as will more compression, boost, nos) will cause the plug loading to go up much like you increased the gap.
If all that checks out, Disco the vac advance, swap the coil, then swap the MSD (in that order).
