90 silverstang, normally I check an intake and exhaust on each side. If I know all the parts are right and the machine work is done right that is good enough. If it's a mystery motor and I don't know for sure what work has been done to the block and heads then you might want to check another cylinder or two. Depending on the cam you may have all one size rods or one size for exhaust and one for the intakes. If it's a dual pattern cam then you'll probably have a size for intake and one for exhaust. You don't need to size each valve. If two intakes or exhausts are that far off from each other something is really wrong. Keep in mind that this checking should be done when building a motor or changing heads, cam or rockers. If you're doing the work yourself then learn how. If your mechanic is doing the work ask him if he does it. If he says it doesn't matter find another mechanic. Mike