The main webbing is only adequate for less severe duty applications, but one thing to remember is that you are planning to push over 4 times the HP to this engine than it was engineered for by GM. 600 HP may not sound like much in today's performance market, but anytime you have a HP level of 2 times the cubic inch, you have a serious amount of stress to all the components, and most require a major upgrade even down to the smallest and obscure of parts and also to detail to ensure it will survive. For example, 2 HP per cubic inch for a 350 V8 is 700 HP, and for a 454 is 908 HP. Even though many of those V8 blocks were over-engineered for racing and High Performance use with 4 bolt mains and higher nickel concentrations in the castings, even then, those factory blocks won't live at those power levels for long.
There have already been guys racing these blocks at HP levels not that much higher than what your planning that have already experienced the blocks splitting length-wise front to back between the cylinders due to extreme cylinder loading from high boost levels because these blocks are thin in that area by design. And custom components have been made to help reinforce the block between the cylinders to keep them from self destructing. The main caps will walk in the cap registers in the block and need to be doweled and/or better main caps installed(billet and/or 4 bolt main). Maybe you have seen illustrations in Leo's book if you have one, showing these mods and others, but they have been put into practice for necessity and not for show. A main girdle would also be money well spent along with better main caps. You are basically just trying to keep the engine from self destructing at this power level and beyond. And this is really just scratching the surface. Remember that whole other world of machine work I was mentioning, well you have now arrived!LOL
I would suggest trying to start your build with a Mexican block if you can find one, they are a lot thicker in the cylinders and will be a better platform to begin with. You'll still need to perform all the things to those blocks as well. A fully counterweighted crank is a good idea also. Do you already have a turbo selected for this build? Are you planning to use a carb, or EFI? Lightening the crank is fine, but lightweight components like pistons, wrist pins and rods will not live at these levels of output for long. That is a common mistake that many novice engine builders make when building high output engines such as this. For a street engine that is relatively low power they are fine, but at some point of power output the lightweight parts will fail and you need to go back the other way and get beefier. Any idea what the average Crower or Carillo brand 9000 RPM Winston Cup Super Speedway connecting rod weighs? 830 grams. When you start combining street driving and high HP builds like yours, think NASCAR engine build, not Bracket Drag Racing or life expectancy will suffer drastically.
