I think the original equipment plug was an AC #45. A slightly hotter plug would be a #46. Colder, 43 or 44. The 43, 44, and 46 are not being produced now, so 45 is the only AC number currently available at most FLAPS. Don't substitute a 45T or 45TS- - - -they're tapered-seat plugs for later model engines, and they don't have a ring gasket.
Champion and Autolite have plugs that cross-reference to the AC numbers, so it might be necessary to switch brands. Original-equipment AC's still show up on Ebay occasionally. If you can find a set ot C-45 plugs, they're the commercial type that were used for delivery trucks, taxicabs, etc. The electrodes were bigger, and those plugs would last a lot longer. I used to run C-43's in the dirt track car with a warmed-up 327, and I could clean and re-gap them several times before replacing them. Regular plugs only made it one or two nights of racing before needing replacement.
Jerry
