[crazyjeenyus]

My two cents:

Its virtually impossible to know the extent of the damage without opening it up. I wouldn't consider anything short of a full tear down. Take the block to get checked for cracks in the webbing. Irregular vibrations at high rpms can cause all sorts of problems.

If the block gets an OK from a reputable shop, you've got a clean slate. At that point, if you're looking for 400hp/400tq you may as well go with a longer stroke rotating assembly. You could even get a 3.875" crank and build a 390 (std bore) or a 395 (@ 4.030" bore).

You'll likely want new heads and valve train to provide better flow. Personally I like Holley carbs, but they're are several good options out there. You may even consider an EFI system. My brother put a Holley Sniper kit on his '68 Firebird and he loves it. It's self-tuning and the car runs much better in the cold weather.

I'd have a hard time sleeping if I rebuilt a motor without having it checked for cracks first.