basically, in order to see the gains the higher ratio roller rockers are capable of you need a good flowing exhaust - so the extractors should come first.
installing the rockers would still see an improvement if you where to do them without having extractors, but its a case of having all the supporting gear (good intake setup & good exhaust setup) in place in order for them to see full potential.
with the extractors - if they dont come with a new y-piece (most dont!) then get one custom made when the extractors go on. if you have a look at the shocking press bent stock one you'll see why....there's no point having good extractors if the flow is getting choked going through a tiny y-piece after them.
Quagmire: My fellow Americans, I have not been entirely truthful with you. I did gagoogidy that girl. I gashmoygadied her gaflavity with my googus. And I am sorry.