I went to the trouble of tracking down exactly what the right plugs were for my heads, and then the additional ass pain of tracing a straight line through which brands no longer offer a plug that'll fit.
The summary of two week's off-and-on reading is this: if you have 2.0 bus heads with the oval exhaust ports which dump downward, the ideal spark plug is no longer available from anyone.
Some old man in a snap-brimmed hat and churchwarden pipe must have hoarded up a pile of them in a hollow tree somewhere, but you can't shake any new ones loose for trying.
There appear to be two acceptable substitutions, one a get'cha-by grade made under the brand name Autolite, and the other still legitimately made by Bosch. I like the Bosch, since they never seize in the sockets (ever) and they have a better-appearing edge on the washer that serves as a gasket.
I have now used four different plugs in my engine, with various results. Personally, I really liked the Bosch 7900 W7DC Super plugs that were in it when I got it. They were replaced with NGK BP6E S plugs, also a fan favorite -- but neither is available from anywhere in the US without going through eBay or some such process.
I'd buy a lot of different things through eBay before I bought potentially the wrong spark plugs. I must be wierd or something, but I don't suspect I'd get the right parts. Call it a hunch.
Autolite's available plug is enumerated as Part No. 4265. It is recommended to be gapped anywhere from .25-.034". I gapped at .34.
Bosch's available plug is the 7900 WR7DC+. Same specs for gapping in the Type IV as the Autolite plug, and I gapped them at .34 also.
Interestingly (to me, and maybe nobody else), the major difference betwixt the W7DC Super and the WR7DC+ is a resistor which helps to minimize whine through a car's stereo system somehow. Otherwise, they're exactly interchangeable.
The difference between the Autolites -- which I only installed new at the beginning of last week -- and the Bosch plugs I just got IS noticeable. There's a sharper pitch to the exhaust note when I crack the throttle, and the car (which has always had great launch from a standing start) now cracks your neck like a Catholic nun slapping a daydreaming kid's knuckles with a yardstick.
I hope that helps somebody.
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