As Hink and advanceengin said. The typical 400 stock block will only have a .150 wal thickness average when bored .030 over. Some builders will sonic test them and shift the bore a little to inprove the wall thinkness after bored. They also ran hot in stock condition IE the steam holes from the factory. Filling the block to the water pump is almost always a No,No for street driving but comonly used in racing applications, but will usually run hot on the street if driven any distance. I think Hink stated in a different thread that testing 6 blocks he could only find 2 that would bore .030 over due to core shift. Sometime the walls can get as thin as .080 tk. due to rust away from the inside, don't forget these blocks are 30 or more yrs. old after boring .030, not good and will run hot and be subject to cracking.
JMO
Zip.