The energy that is stored into a coil, and that comes out in the form of a spark, is proportional to the primary inductance of that coil times the square of the momentary current shortly before this current is switched off. From this equation you can see that a good match of the electronics and the coil can be very beneficial in terms of spark strength.
We advise, NOT to experiment with old coils, as a coil that still looks good on the outside, tells nothing about the inside.

Proper wiring is important too. Long wires to the battery, or worn contact switches can limit the energy delivered to the spark plug.