Soo, I have a 1953 Chevy 3600 with its original 216. My question of the day is: on the intake/exhaust manifolds mounting bolt .....keepers i quess, there is the letter "F" stamped in the metal. (it's the things that the bolts go through to hold on the manifolds on the engine), are these dirrectional? If it wasn't for all the crud on everything I would have noticed the "F" when I took them off. Just want to do it right the first time.