HEAD INTERCHAGABILITY. LS1 and LS6 blocks will only accept LS1, LS2 and LS6 heads; LS2 blocks can use LS1, LS2, LS3, LS6, LS9 and L92 heads. LS3 and LS9 blocks can use LS1, LS2, LS3, LS6 and LS9 heads. LS7 blocks can accept any LS head. One other difference to note is the LS9 block uses 12mm head bolts while all others use an 11mm. ROCKER ARMS The LS2 uses the same head design as the LS1, casting number 241 for ls1 and 243 for the ls2. the LS2 had some minor changes porting etc to increase flow, but was not enough to match the flow figures of the L98 superior heads. Walesy- how many times in the last few weeks since i brought this to your attention have heaps of "experts" been wrong.