For the XP cam (I know you are going with that one) you NEED 105# springs. It is FAR too aggressive for LS6.
STOP TRYING TO DO EVERYTHING ON THE CHEAP, IT'S GOING TO FUCK YOU.
The LS6 springs are ~90#
If you want 105# springs, buy the Comps. They are better quality and not much more expensive.
Don't do everything bottom dollar, Carl. It's going to fuck you in the end.