AC 44 plugs are still available, by the truckload! We use 43's and 44's on the race engines with the early-type cylinder heads all the time. You need to find a better parts store, preferrably one that caters to professional shops, not do-it-yourself tinkerers. Platinum plugs are just sucker-bait. They don't really do much other than separate you from more money every time you change plugs. The Champion premium plugs with the black insulator might be worthwhile, as they're designed for delivery trucks, and other heavy-duty use. A good parts store should have an interchange chart which will let them choose the correct substitute for the original-equipment AC part.
Jerry
