It all depends on what you are looking for and what is in your budget. If you have the bucks, build a 400 plus c.i. motor. The larger bores will take advantage of the aftermarket cyl. heads. The stock block 400 has been a choice for yrs.,before there were Dart blocks or World Products blocks. If you do not go beyond 4.155 bore size and do not put too much juice to them they hold up. I had the opportunity years ago to work on a Sony's 500c.i. small block based on a stock block 400. By today's standards it would be considered rather crude but that was all that was available. In limited performance applications a stock 400 block is still a valid choice, especially in the 2 bolt version. To address the argument 406 vs 383. I would choose the 406, not because "Bigger is Better", but the 400 block can take advantage of the aftermarket heads that are now available.