Well i am getting to the head section of my build up on my l98 tbi 350. There is a little problom that i see and was woundering if maybe i can do it or not. Well my question is, on the valve seals of the head there are the intake (rubber) and the exhaust (plastic). My question is why, plastic and rubber, Why not just rubber? Can just rubber be done?

Also at my local parts store there are two types of rear seals, i bought both of them but dont know which one to use? One is rubber, And the other is some type of weard matireal, Witch one should i use. Thanks eric