Sure there is less webbing in a four bolt block, go splayed in a two bolt block, but make sure the cylinder stays in round when they hone it. In other words, make sure the mains are torqued down when they bore/hone to make sure the cylinder isn't deformed after torquing the splayed bolts. And on another note, the big issue here is that you don't want any side play or 'slide' of the cap. The four bolt block will just 'hold' it with more bolts. The new LS1s have 6 bolt mains from stock just for info sake. For you, I would stay with the 2 bolt unless the 4 was nearly the same price. The crank and mains I would leave....the rods however....