I use NGK's BP6ES - which is equvalent to Champion N9YC (standard 1275).
The DENSO alternative is W20-EPU.
Copper cored, with U groove in earth electrode for bigger flame Ďkernalí.
Original equipment for Nissan/Toyota/Lexus/Subaru etc
BP7ES/N7YC/W22-EPU is a colder plug for higher compression/competition use, stage 2 & 3.
BP8ES/N6YC/W24-EPU is even colder only for race use.
The gap should be 0.025 in (0.65 mm).
Good information about sparkplugs can be found here
Finding an initial setting
1. Take the rocker cover off and the spark plugs out, now jack the car up until 1 wheel is off the ground. Put it in third gear and turn the engine over by turning the wheel thatís off the ground.
2. Now watch number 4 cylinderís inlet and exhaust valves, keep turning the engine until you see the valves rocking (one closing as the other opens). Find the point were they are both shut. This is where the exhaust stroke has just finished and the induction stroke starts on No.4. This is also top dead centre on the firing stroke of number 1 cylinder Itís a good idea to now place a screwdriver blade across the flange of the dizzy and block tapping it with a hammer to mark where tdc is. You need a mark on the dizzy and the block to give a reference point. Paint or Tipp-Ex can also be used to make a mark.
3. Have a look at the rotor arm it should be pointing at number 1 spark plug (or there abouts). The timing mark on the bottom pulley should also be somewhere in proximity to the marks on the timing cover. Refit the distributor cap and the car should start. When you get it going let it warm up for a few minutes then set the tick over to about a 1000rpm.
4. Now with the engine running and the dizzy bolt/clamp slackened off turn the dizzy until you find the highest tick over possible. Now again turn the dizzy anticlockwise until the stamp you have already made on the dizzy is about 4mm around from the one on the block. This will not give the right timing for your engine but it should get you running and then you can get it set up properly by a rolling road or someone with a digital timing light.