At the power level produced by a stovebolt six, even a modified one, I don't see an advantage to ductile iron over plain steel. Those Milodon ductile iron caps with the angled outboard bolts are for engines that are on the ragged edge of blowing the crankshaft out the bottom of the block. The primary purpose of a wider, taller main cap with multiple bolts is to reduce the flex of the block under high speed- - -high stress situations. The only reason I'm considering doing that is to add a little rigidity to the middle of an engine where I'm going to be running a much smaller diameter main bearing than original- - - -converting 235/261 crankshafts to run 400 small block V8 main bearings from front to rear- - - -all the same diameter. They're MUCH less expensive and more available than the original mains.
Jerry
