Newbie needs 273 spark plug help

Hi,

I just joined FABO and posted a brief introduction in the Welcome Wagon forum. I'm very happy to be here and looking forward to learning from all the A body experts. I just bought a stock 1965 Barracuda Formula S with a 273 Commando and 904 automatic. This is my first technical question on the forum, and appropriately for a newbie, it's sort of a dumb question:

What spark plugs fit a stock '65 273 4bbl? It has the original 10.5:1 iron heads. I failed to find any plug specs in the service manual, though I'm sure it's there somewhere in the 700+ pages. When I enter the year make and model on car parts websites, I get all kinds of different plugs. Some are 3/8" reach (length of the threaded part of the plug), some 3/4". Heat ranges are all over the place. Some are even non-resistor.

I'm particularly concerned with the reach length. I have domed pistons and I'd like to avoid turning the Commando into scrap metal on start up!

Thanks in advance!