If you use it, definately fill it to the bottom of the water pump with ROKblok block filler, by far the best and easiest block filler to use, just make sure you follow directions, mix it soupy, and work fast, as the stuff WILL set up really quick. I would also definately have 4 bolt splayed caps installed. Which, then at that point, a SHP block from Dart, may be the way to go, then you can skip the block filler. I personaly won;t use stock 400 blocks anymore, for anything more than 450hp street engines.
Frank