Just an FYI for others in the same situation: I was working on OMC Cobra with a 351 Ford Windsor engine and to say the clearance was tight is an understatement! None of the sockets I tried could get in there, even a tapered one. I finally broke them off to remove them. (It was that or remove the exhuast manifolds.) My local auto parts store had what is called "header plugs" made specifically for tight fits like this. They run the same heat range and the only real differnce is they are MUCH shorter and went right in with zero hassle.