NGK has a real tech guy that answers on second ring --he will put you dead on with a plug part number all are about $19 a set off Egay with free shipping and if in a jam Advance Auto parts can get overnight for decent price.
Thing is with NGK the plating used on the threads makes good tuning aid--we run alky and when we get that plating burning off a couple threads up then we are dead on
NGK quality is second to none. I do like Autolite race plugs but for the money no way I will swap from NGK--I would not take a set of Champion junk plugs for free--usually hard to get 8 out of the box w/o one being fubar'd up with off center etc
NGK 5671A then select heat range number 7-8-9 etc and away you go Hands down best plugs year after year Japan made--awesome quality plug after plug

The China Autolite street plugs were awful--but they have switched back to Mexico and quality went way up--if buying Autolite street plugs do NOT accept any with China on the box--even the threads can be twisted and bad on those like they were hand done with worn out leftover WW 1 Russian dies