Since the common replacement coil now is the 584477, I think it’s safe to say the 580321 cap is the correct one to compliment it. I’ve heard before that motors with long plug wires might benefit slightly with a cap with a slightly higher uF rating though.
Over capacitance and under capacitance are both hard on the points. One transfers metal from the stationary point to the moving point and vice versa and I’m sure the OMC engineers took this into consideration when specifying which cap to use. Since the classics are not race motors which get tuned frequently, reliability and longevity between tuneups was probably a priority.
Here’s something from a 1980 Johnson parts book. Note how the RD 18 – 23 motors originally used the 580197 coils but called for the 580321 caps. It looks like the FD’s had the caps and coils juggled around a bit to. Confused yet?
