I have an 89 454 365 mild build. Heads cam msd etc. I want to put new spark ugs in. So right before I bought the boat the guys son decided to put stock ac delcos in. When I bought the boat there had been a plug rolling around in the bilge. Was an ngk that I could see.
The edelbrock heads say to use a rc12yc champion, I crossed to an ngk bkr5eix iridium. Well I went to put them in and finally could reach the ngk rolling around and it was a R5671A-8 Racing Plug. Completely different heat range etc. So I'm not sure what to use with the build, racing plug vs iridium and what heat range? What's the stock heat range should i be greater? And what are the iridium laser point ones?

I would use the champion plugs the heads say as a baseline. If it works good and seems to be correct heat range you can switch to iridium's if you still want to. They are cheap plugs.

Well whatever was in it seemed to run OK. I should verify what acs I have. But if i can get it to run better why not toss in beter plugs. The heads said those champions or equivalent. I just got the boat last year. And those plugs are 1 season old. The motor was out and done and the hull bilge all cleaned up 2 years prior. So I'm assuming the ngk was in there until his son messed with it. The motor was done and installed by a builder/marine mechanic

NGK BKR6E
or NGK V Power BKR6EYA
They’ll add 37 horsepower (sarcasm)
Everyone has an opinion, that’s mine. I pick ‘6’ because 6 is usually a safe heat range.