1200GXman, you can always replace standard plugs with platinum equivalents, for any engine -- even a lawn mower.

To set your expectations, they are not going to increase your fuel economy over a new set of regular plugs.

To increase economy, use the stock Hitachi carburetor instead of a weber. If you have a weber, jet it slightly lean all around. This is where a larger gap will help, to fire the leaner mixture. With stock ignition, I recommend 0.035 inch gap (8 mm is the Nissan spec, which is only 0.030). This bigger gap should smooth out the idle on a stock A12 just a tad.

Yes interesting topic relating to the more finer details of good engine tuning, thanks for the input.
New head is on! Idles very smoothly on 1000-1100 rpm, idle noise at the exhaust sounds very nice.
Off to Mike Vine dynotuning on Tuesday next to see the difference the new head/roller rockers have made to the power output, pre-dynotuning its wicked!!
An idea of what the roller rockers have done for valve train: Lift at valve was just under 12mm, now just below 16mm (later dimension was done pretty crudely, will do more accurately when i take the tappet cover of to re-check tappet clearance)

Lemonhead

Congratulations.
Let us know what the dyno figures say.
I am VERY curious.
What setup is your engine again? I cannot remember.

DDgonzal.
I have the Hitachi SU's.
December I am going to remove them and clean them up inside and out.
Going to tune them as best as I can and maybe slightly leaner.
Going to make my gap then 1mm instead of the standard 0.8mm on the plugs.
Is 1mm a bit too large?

Ddgonzal
I was going to say that 1200GXman has a genuine GX engine with the twin Hitachi's This is an excellent setup as i was able to pull high 30's per [imperial] gallon anytime i took my GX powered 1000 sedan out for a drive.
I got better than 40 mpg when driving for economy at an average of more than 70 mph on a 250 mile run one night when going to the Bendigo [Victoria] swap meet.

I got better than 50 mpg when i drove for outright economy when i went to the Ultralight fly-in in Holbrook [NSW] about ten years ago. Yes, it was a slow trip. The GX is a superb engine. Plenty of pep, plenty of economy. It's all in how you drive it.

1200GXman
Try setting the plugs to .9mm & see how it runs. Put your hand on the coil at the end of a drive to check the temperature. If it does not raise blisters on your fingers, then it has not overheated yet. If you get any misfiring, think about using a 'sports' coil. Bosch marketed the red coloured GT40 coil [40,000 volt max output] in Australia & these provided more voltage when it was needed.

If all goes well, then try 1mm & see what happens. If you suffer misfiring at full throttle & full load, then you need either more volts [sports coil] or a smaller plug gap. The bigger the gap, the higher the voltage needed to fire it. The higher the compression pressure, like at max torque, the higher the voltage needed to fire the plug. Continuous high outputs build heat in the coil. Excess heat kills coils, so a sports one really is a good idea. Make sure that you get either the resistor type [GT40R] or the regular non resistor type, whichever is correct for your car.