4 bolt mains don't mean anything unless they are splayed and doweled. thats the only way to keep them from moving around. the BBC merlin blocks with ductile iron caps without dowels have cap walk too. as i said before, splayed and doweled is the way to go. we routinely see merlin and dart blocks holding up to 1800-2200 HP without cap walk. don't you wish a mopar block would do that.
if it's worth doing it's worth doing right. don't skimp like MP did and have a heavy iron block that still has issues. it would be a waste of time and money in the investment and the same for the end user IMO.