Quote Originally Posted by popeyenate View Post
ls6 springs, maybe new retainers and locks
Definitely new retainers. If you switch to LSx style springs, you need LSx style retainers. Running stock retainers on LS6 springs would give you a max lift of .500", which is nowhere near enough for the XP, plus the pressures would be so high you'd destroy the stock timing chain/dampener in short order. Stock locks should be fine, though.