Steel expands at a different rate than cast grey iron does, same thing on aluminum main caps, the expansion rate and holes in them do not expand the same as the cast iron does
Hence my preference of using cast ductile iron
I had three RB blocks with cracked main webs
The 400 blocks are way better to start with than any OEM 440 block for any build that you want to make more than 600 HP on pump gas or above 650 HP on race gas