Probably the only reason to replace the stock coils is when the output leads crack or are damaged. It's pretty rare they fail internally without some sort of physical attack upon them.
They work quite well with the stock dwell on the points cam. The stock ones are about 5 Ω. So, if you retain points, keep the primary resistance at that rating.
Don't be fooled by claims that different coils will boost the spark voltage in a running engine and the ravings about all the wonderful "benefits". That's just salesmen hawking their wares.
If you don't increase the engine's compression, higher spark voltage is unnecessary. And, if you don't increase the spark gap, you won't realize more voltage at the spark gap. (assumes a Kettering type system (stock) that relies on the coils storing the energy.)
While a lower ohm primary coil may be capable of more voltage, it won't be realized in the SOHC4 due to the way the system works. A lower ohm coil WILL consume more power from the bike's electrical, though.
Cheers,
