its shims and pushrods. so i would guess it gives you shims to put the rockers at a better angle of attack (for the valve guides to last) and gives longer pushrods to make up for the distance. or you could call thunderracing i bet they know.

 

talked to yt. They said they will replace the whole set as long as I can find my invoice

 

Cool deal, glad to hear that they're doing the right thing

 

glad it aint the springs cause i just bought a set