.003 to .0035 bearing clearances especially on the mains work just fine, using a thicker oil, say 15w 40 or 20w 50. If using a stock block on a 600 to 700 HP build you want the bigger clearances to help with the mains and the caps moving around under power. If you have tight clearances, the wiggle will cause a bearing to spin, when the crank wipes against it and pushes the oil out of the way. Got to remember those stock blocks were designed for 400HP, so if you increase the power level 70% or more you are really loading the block. All the NASCAR and Prostock engines using those super thin oils, have very rigid blocks, no wiggle. If you look at all the newer V-8's they are designed with a very rigid main cap set up with multiple bolts a lot like aftermarket blocks.