A stock 400 bloch is fine for 450 hp, providing it passes sonic test and magnaflux. Pay special attention to the area just above the lifter bores on #1-3 cylinders. They love to crack there. The steam holes are another spot that they crack.
Be sure to also do the following with a stock block, prepping for 450 hp.
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Line hone/bore seal surface, stock caps with studs are fine, 2 or 4 bolt.
Plug the steam holes in the deck, use crack repair plugs. You will never run it at temps that will generate surface tension that will make steam pockets. Unless you're going to use it in a truck that will run at 220°, plug them.
Check and correct camshaft bores if required. Index may be off, size is occasionally off. Number 4 bearing bore is sometimes too big.
Index and bore lifter bores for .875" lifters. Some will probably require sleeving.
Square decks to mains/cam bore.
Bore and hone with torque plate, referencing them perpendicular and parallel to the crank centerline.
Use sonic test data to move cylinder placement if required. Trying to index them is a battle you can't win,
Short/mid block fill is very helpful for cylinder stability. You will not have cooling problems.
Correct and index dowel pins for the transmission to crank centerline. BHJ tooling.
Clean up the casting flash for the oil returns in the rear of the lifter valley.
Plug the thermostat bypass hole in the front of the block.
Minimumally chamfer the bores. Chase and chamfer the head bolt holes. Use a thread cleaning tap, not a regular tap.
If you don't skip any steps, you'll have a solid foundation.