The factory installed NGK Platinums are a VERY good plug and really are the preferred plug. If you need something less expensive for the time being you can use copper plugs but they have a significantly shorter lifespan. I like NGK's iridium plugs; They cost the most of the three but are long lived and consistent. I generally recommend people stick with NGK's regular platinums for a stock engine.
I do not recommend any other brands unless you specifically measure them. There are two different standards used for spark plugs and the size difference in insulator length can cause problems. Autolite's, for example, use the ISO standard and as such the insulator is around 4 or 5 mm shorter than that on the recommended plug. This can lead to shorts to ground with plug wires that are older or aftermarket plugwires with a looser boot.
NGK's plugs come pre-gapped. Do not try to re gap platinum or iridium spark plugs unless you've got the right tools... they are very easily damaged! Always check the gap though and regap copper plugs if needed. Additionally, there IS a big difference in the specified temperature and gap of GE plugs versus GTE.... make sure you get the right ones.
Spark plug shims or indexes aren't a bad idea but are unlikely to return any significant gains on a stock 7M (GE or GTE). If you feel like taking the time to try it out feel free, it's not going to hurt anything.
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