I agree with fever get a nice aftermarket block if you can afford it. I had to go through 3 400 blocks before I found a good one. With those short rods in there the outside cylinder walls catch hell. The bad blocks I found all were wore out .020 on the outside wall only. I didn't want to go .060 on a 400 block so junked em. The guy I had doing my machine work, Hotards just happened to have a good 4 bolt 400 block. I didn't really want a 4 bolt 400 block but just couldn't find a good 2 bolt block. So far so good with the 4 bolt block, but I'm not put much of a load on it since I have it destroked to a 377 using a 350 crank.
Good luck on your find. I wish now I would have put more stroke to mine, can't beat the torque on a true 400 or larger stroked engine.