I'm with (Hink) on this one if you can afford it. The SHP block is definately safer at .60 over. My good friend Jimmy Smith a member here also runs a 358" and has gone thru a couple blocks in the last 2/3 yrs. One he pulled the main web out of it and has split cylinders on the other. The SHP block will seal better on the cylinders due to the extra wall thickness and make more HP without filling the block with block fill.
I've got a Dart lil M for the 434" engine that's going in my car this winter.
JMO
Zip.