If you just want an LS1 kilr, then Nitrous will do it man
In the 99, just gets gears, exhaust, and maybe a good CAI and a tune. And the driver mod should set you at mid 13's man
In the 89, do a bit more if you're willing to man. You should be able to find some GT-40 heads for probably $450, and a good intake for $300-, then install that cam, some gears, and exhaust
:disclaimer:
Without the driver mod, NO mods will give you an LS1 killer
-Will