These main caps, whether they be for 2-bolt to 4-bolt conversion, or you're replacing the factory straight 4-bolt caps with the Milodon straight, or angled 4-bolt caps, you're increasing the strength of the block. Because the angled main caps place the side loading to the outside of the block, the caps are located against the main cap register in the block preventing cap "walk". Milodon main caps have more cross-sectional strength due to the high-strength ductile material and yet they aren't so rigid that they transfer shock loads to the crank and bearings. The center three main cap kits come with all the bolts, washers and drill bushings needed. Block machining is required for final installation.