The problem is the 'significant difference',
which is the current, not the voltage cannot be measured easily. That is why the coil should be matched to the ign system. The original HEI coil had a 0.6 ohm primary, so a coil around 0.4-0.6 ohm s should be used.
You can use a factory canister coil that has a 1.5 ohm primary resistance, & if it has a high turns ratio will through a long spark. Looks great, eh!!!
But the spark will be low on current, & it is the
heat in the current that ignites the mixture. The spark duration is also
shorter.
Use 0.060" plug gaps with good spiral wound leads. GM specified 0.080" gaps for some engines.
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