Advaned Auto parts GENIUSES!!
I guess I've been lucky, I just picked up a set of plugs for my 67 from Advanced Auto. I explained it has a 70 318 and he had a set on the counter in seconds. I usually deal with a local independent and he'll search for any parts I ask for. NAPA let me down only once and it was a brake pro hotline who swore all master cylinders were the same in 67.