I'm running the Patriot 243 LS6 64cc heads with a .588" lift cam. What is your cumbustion chamber size and what gaskets did you use? The stock LS6 heads have longer valve stems. I actually have that magazine here at the house and had my doubts so I had to perform some clearance checks. A major difference between 385-horse and 405-horse LS6 cams is the base circle radius. The base circle for the ’01 LS6 is smaller than that of the LS1 and the truck cams and, for MY02, it’s even smaller. Most Gen III cams have a 19.7-mm. base circle but the ’01 LS6’s is 19.3 and the ’02’s is 19-mm.. Both reductions were to accommodate increases in valve lift. My concern would be the valves in the 02 and newer LS6 heads are 0.6-mm. longer than the valves in all other Gen III engines to accomodate the base circle differences. For this the reason I went with Patriot heads and LS1 valves because I didn't want to end up with a set of 243 heads that had longer valves. I'm no expert but I did alot of research before my swap.