Vortec heads use press in rocker studs that can pull out when you install heavier springs.
Heres the cheapest and easiest way to pull and tap your own studs without having to machine down the bosses! No expensive cutters needed
Pioneer Stud Part# RM-348-16
https://amzn.to/3yKK3Id
***Be sure the Tap is Straight***
*Use a sealer/loctite on the studs
*This style of stud still does not use guide plates, so self aligning rockers are still needed
*This has to be done with the heads removed from the engine*
*Heat may be needed for extra tight studs, or you'll crack the stud boss*