550 HP is right at the limit for a stock block and 600 is pushing it. You should be using billet main caps and a mains girdle at that more level in a stock block.
Or, just build a turbocharged slant six. There are a couple of those engines whose owners frequent this BB whose engines make around 500 HP without anything in the way of main bearing supports, or girdles.
A turbocharged slant 6 is capable of mid-10s in a 3,000-pound A Body, partially because the engine is about 100 pounds lighter than a normally-aspirated 340/360. With aluminum heads, intake, and lightweight headers on the V8s, that may not be true.:sign10:
The head on our /6 car weighs 84 pounds! Sure wish somebody.... ~ANYBODY~ would come up with an aluminum head for this thing.... even if it didn't flow any better that the cast iron one.
