Hotrodpaint. Thanks for the info. If we take the 340-409 we would use better heads and go with some deep dish pistons and probably with a more agressive cam. Should be able to get 500Hp. as far as width, your right on that and my 37 engine bay is not that big, but I have 2" of clearence on both sides, not much but enough. The only problem is, I'm concerned about is the heat buildup. On the 400 block, to be honest I've never worked with one and heard that they overheated because of the piston location. True or not?