mitch500- you should take off one or more of your existing plug caps and measure them with an ohmmeter. You can get them off by unscrewing them from the end of the wire. You should measure about 5 thousand ohms (5K ohms). This was the norm for Canadian sohc4s, to have resistor caps. Then the Honda recommended DE8A plugs would be the correct choice.
If someone has replaced the original caps with non-resistor caps (thinking somehow that they would have a better spark) then you would see a resistance of only a few ohms. Perhaps this is why you have the NPR8EA plugs installed.
Resistors in the plug leads, the caps or the plugs (or all three) where starting to become common in the 70s as manufacturers realized that adding a bit of resistance in the spark secondary circuit would reduce interference with AM radio without affecting spark strength. This is less of an issue for us now. Having resistance in more than one of these was not uncommon. The way our bikes were built, the HV wire which in molded into the ignition coil is solid (non-resistance), the cap is resistor and the plug is non-resistor. You will not be replacing the wire without some difficulty, just the cap.
While you have the cap off the wire, you can also check the condition of the end of the wire. After forty years, the wire insulation tends to split and the wire itself may be somewhat frayed. Whether you get new caps or not, you can often improve the connection from wire to the cap by carefully cutting off only about 1/4" of the wire thus giving a new "end" for the plug cap to thread into.
Good luck.
