you want to go with a copper thick blade plug 2 degrees colder than stock.
you're stock are a RC12YC
so look for a RC10YC - cross it
I use Autolite plugs and went copper, colder and gapped smaller for my supercharger.
The standard copper part number for the Champion plug for the LS It is an RC12YC or an RC12YC4.
- The "R" means it is a resistor plug.
- The "C" is its shell style - a "C" shell type means a 5/8" hex with a 14mm thread dia. and a 3/4" reach.
- The 12 is your heat range number, usually in increments of 1.
- The "Y" and "C" are your electrode designs, in this case the "C" stands for copper electrode, and the "Y" is for a standard projection.
- The last number is a generic gap, this is done for ease of installation, so a 4 in this case means a .40 gap (the LS calls for a .44 gap).