If you look on the bottom of the block of the 4 bolt main on 400's, you can see why those blocks aren't the best for racing. The outside bolts of the maincaps hardly have any material around them and the block is prone to cracking. However for a street application this would be fine, as long as you keep it mild on the boost I'm sure. The two bolt main 400's are a lot better, the main caps are wider than other small blocks already, plus if you ever were worried about spinning bearings you could always get 4bolt splayed maincaps and machined. The two outside bolts are at an angle so they go into a part of the block where there is actually material there.