Did some quick searching and using these 2 webpages I verified the correct stock P#'s from NGK & Denso:
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DENSO SPARK PLUGS
Considering your going for 50hp more than stock, and 'mostly' going for an everyday capable car with more fun I'd say go one heat range colder to start with. IF the plugs seem to show signs of being too hot, go to 2 stages colder.
Platinum plugs
Stock - NGK: BKR6EP-11 / Denso: PK20R11
*1 stage colder - NGK: PFR7G11 / Denso: PK22PR11
*2 stage colder - NGK: N/A / Denso: N/A
*= part # is the closest I could match to the design/thread/length/tip style & gap, but may not be 100% exactly the same as stock except for the heat range.
Iridium plugs
Stock - NGK: BKR6EIX-11 / Denso: IK20
1 stage colder - NGK BKR7EIX-11 / Denso: IK22
2 stage colder - NGK BKR8EIX / Denso: IK24
Notes: on the 1 stage colder you may end up wanting to go with .8mm gap (ie p# BKR7EIX ) since it will be going into a force inducted motor to help prevent spark being blown out, if that's a problem. Also, the 2 stage colder BKR8EIX is only available (with the .8mm gap; not that having a slightly smaller gap will be much of a problem, may help as said above).
Suprisingly enough (IMO) the 3s-gte uses the same heat range sparkplugs as the 3s-ge including the beams motors, just different gaps... But then again considering the lower compression it may not have had high enough temps to cause problems.
Andrew
p.s. Blacktop & Red/Greytop use the same sparkplugs, so these are also applicable to the blacktop guys if looking for colder plugs...