The 400 small-blocks are a different animal. They have larger main journals (2.65 versus 2.45 inches), and the main caps are the same width in both the four-bolts and two-bolts. The important things here are a good align-hone job and quality fasteners. (Note: I have both.) The difference between the two- and four-bolts is in the main webs of the block. The two-bolt blocks actually have a stronger main web area than the four-bolts do. If you plan to build a nasty 400, start with a two-bolt block and install aftermarket splayed four-bolt caps. A properly prepared two-bolt block will hold up to 500 hp.