I'm no specialist with these motors or LSx motors... but I will settle this as only a GM Parts Guy can. Both the L32 and the LS4 use the same iridium spark plug, a 41-110 (GM# 12621258). The TR55 is a direct replacement for either plug... slightly cooler but a direct replacement. So GAP the plugs down to the right specs for the LS4 and you should be golden.