I would start with D16Z6 plugs.
NGK ZFR5J-11
ND KJ16CR-L11
Install one and rotate the engine once, pull the plug back out and make sure the gap hasn't been closed by contact with the piston. (It shouldn't) Then you are going to have to run the car and pull them back out to "read" the plug. (again, just a precautionary measure. This should be the right heat range)
You don't need to spend extra money on Bosch Platinum + 4s or NGK Irridium. D series plugs are too easy to replace to need an extended life plug and I already wasted money to not notice any difference in performance. Avoid Splitfires. My D16Z6 ran like crap, lost 10-15 mpg, and other CCers have reported melted electrodes.
You'll know you have a half ass decent guy (or girl) at the parts counter when he (or she) doesn't balk when you give them the above numbers. Parts stores stock plugs by a 4 digit number. If the parts person just goes and gets the plugs, he's good. Looks them up in a paper catalog, he's old. Looks them up in the electronic catalog, he's ok. Stratches his head and says, " We don't carry those kind of numbers..." skip him.