Yes, so as I thought stage 3, not 1

Standard gap is 0.25 in (6mm) but then... that is for a standard engine, which yours is not.

Do you know the ignition system is in decent order, so leads, rotor, cap etc. It all has to be perfect to stand a chance of being half decent on a tuned car.

If so you could try dropping the plug gaps slightly, which isn't ideal.

One easy mod you could do if all else fails is purchase a GRP A coil, which has a higher output.

Nirvana here is wasted spark, but that does not come cheap and not necessary in my experience.

Martin