Help Choose new Plugs for worked 360
If I wanted another brand I would just cross whatever Champion number was correct and go with the stock plug in another brand.
Those of you going to colder plugs are makin a mistake. Colder than stock heat ranges were for engines with high compression and even then were only a couple of steps colder. They were also used in much better fuel without ethanol and with lead to help with spark knock resistance. I wouldn't use anything except the stock plug for whatever year the heads are.
Of course aftermarket heads are a different story. You should use whatever the manufacturer suggests. Even then it's somewhat of a crap shoot, because even they won't know your combination so you may need to swap around until you get the best results.
All in all, people make too big a deal when choosing plugs. Pick one that fits and is the right plug in the book. Done deal.