Here is some NGK Tech Data for reading/understanding their part # designation....
[ame]http://ngksparkplugs.com/docs/tech/design_symbols_plugs.pdf[/ame]
I recommended you a B R 8 E S......as a general recommendation for turning up a SBM with some boost....
Its a Very Conservative Recommmendation, as well.
You may find a NGK B P R 7 E S to be the best.....but heed my advice to stay with a Standard - Copper type spark plug....and dont go any hotter in your experiments than a 6.
GL