[QUOTE=dalorzof;3998637]Autolite site lists various -42 plugs, no AF prefix. Would assume the AF-42's are obsolete. Forget the OEM spec for my 68 390, but a similar story... 40+ year old plugs no longer made.
Don't have a solution on the 351C, but for the 390, they were the BF-32 plugs originally.
A VERY close replacement is still available today - Autolite Racing AR33. They are ever
so slightly colder in heat range. If the engine & ignition are in good shape, you won't have
a problem. They are $3-something a plug but if you're running a 390 at this point in time,
the price of spark plugs isn't your greatest concern.....
As the drill sergeant said, "I taught you everything you know. I didn't teach you everything I know."
"Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so."
- Douglas Adams