My '71's 454" has '66/'67 396"/427" heads that use gasketed spark plugs. I started off with a set of AC Delco R45XLS and it ate them up in only 10,000 miles as their gaps increased about .001" per 1000 miles. I tried a set of BPR6ES NGK's and they lasted twice as long but they too eroded faster than I expected them to last. Then I switched to DENSO 5305 iridium plugs and they now have over 100,000 miles on them with almost no increase in their gaps. If you want spark plugs that last a very long time iridium plugs are the only way to go. Yes, iridium spark plugs cost a lot more but after you figure how long they last they're far cheaper in the long run.