bowtie81 said:
stay away from the 511 and any of the 4 bolt 400's. as said before try and get the 509 or 817.
X2. The 509 2-bolt block with only TWO freeze plugs per side is the strongest of 400 castings.
As for your goals, for longevity of the block and rotating assembly I would recommend doing several things with the block:
1) Fill the water jackets with a good quality block filler to the bottom of the water pump holes.
2) Install nodular iron or billet steel splayed 4-bolt main caps on the center three main journals.
3) Use main & head studs.
4) Stick with a 3.750" stroke. If you run a 3.875" or 4.000" stroke then you will have to clearance the inside of the block quite a bit. While this is a standard operation, it's very time consuming and removing material from the block isn't going to do anything positive for strength. You can easily reach your goals with a 3.750" stroke engine.
5) Stick with a 5.700" connecting rod. If you plan on spraying the engine, you'll get a stronger piston with a better ring package for nitrous use with the 5.700" rod vs. a 6.000" rod.
6) Keep in mind that by the time you find a good useable block, buy the main caps, and pay for all the machine work, you're probably going to have anywhere from $900-$1,200 invested in the block. At that point, you're not that far away from buying a Dart block which already has everything you could want and more. Even the new Dart SHP block would be up to the task for your goals.