Wayne,
Although the LT4 is the latest of the GM crate engines, consider the LS7 as an alternative. It's normally aspirated, so you eliminate the complexity of the LT4's supercharger but a cam and intake swap will put you well north of 600 HP. It comes with titanium rods too. It's a dry sump engine but is quite easy to convert to a wet sump if you want to keep the conversion simple. The LS7 is arguably the pinnacle of pushrod engine development.
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