yeah, replace the plugs and use the "stock" copper-plugs mentioned above....I think the NGK BKR-series has been replaced by the BCPR series now, but they are identical... google it.
I also want to highlight some electric stuff that everyone really needs to think about:
If you check the voltage at the Coil-connectors with Ignition switch in "RUN". Measure from the connector to a good engine ground.
One of the pins in the plugs are +12v constant.... and if you read anything underneath 12v (It should read just a tiny bit less than the battery-voltage), it's a very bad power-conductor to the coils somewhere... not a rare find on old wirings.
It's a nice thing to check the Igniter ground as well.... poor grounding directly leads to terribly bad sparks. Just swapping igniters does not fix a bad ground... Igniter ground vs Chassis/engine ground should not read anything above 0,2ohm's (remember to check your multimeter's internal resistance first though, by just reading the resistance with the measuring pins touching each other) If you play and understand "Ohm's law", you will see how dramatically important good grounds are....especially with Igniton-coils are directly affected by any voltage-drops in the circuits.
Example:
A random coil converts 12v to ~50 000v.
That means that the coil multiplies the input voltage 4166 times.
If you for one reason or another have a 11v at the coils instead (still useful, but things arent good..), it becomes like this: 11*4166 = 45 826v @ the sparkplugs instead.
So 1v less on the coil feed-voltage, equals almost 4000v loss at the sparkplug.
For reference, as far as I remember... old-style coils for Distributor-systems use typically 20 000v for non-boosted applications (most are around 18 000v if I remember correctly)
Thats why Ground and Powersupply to the coils must be in a good shape...as coil-efficiency drops so dramatically if anything is wrong.
