I'm starting a build list on a 400, for mud/sand drags. The only things that I'm shure of is the 400 block with a 6" H beam rod- why because I got them cheap. I plan to buy a 4340 forged crank, either 3.75 or 3.875 stroke. My questions start here. Will a 421 rev and live at high rpm? Will the block have to be clearanced for the 3.875, will the rods have to be clearenced for cam interferance?
I want to get 600+ hp. It Is a 2 bolt block I want to spin this combo to 7000 rpm. Do I need to splay the caps, or will good studs hold the crank true. Can I still use a wet sump, high or std. vol. oil pump? I want a flat top forged piston-(200-250 shot in the future) with a 64 cc chamber for about a 11.5to1 cr. I am somehat on a budget, but will spend $ on a good set of heads. I looking at dart pro 1 platnium 230 cc. Is that too big of a runner for what I am intending to do? Next question is on the cam- I'm thinking around 250-260 dur. @.50 & 550-600 lift, with 1.6 roller rockers. I would like a roller cam, but realy I will probally get a hyd. flat tap. Is that to much for 11.5 cr? Next the carb & intake, I looking at a 830-850 cfm 4150 flange holley, and a victor sr intake. Now with all that said any suggestions or advise. Any input will be greatly appreacited?  

You probably won't find a 3.85" stroke crank, the common "stroker" 400 is a 3.875" stroke. Not much difference, but it could definitely make a piston to head clearance issue down the line...

The stroke difference between 3.75 and 3.875 is pretty slight. Keep reciprocating weight down and durability shouldn't be too much of an issue. If you're still a little uneasy ask your piston manufacturer about anti-friction coatings on the piston skirts and or wristpins.

You may have to do a little clearancing, but you will determine that when you mock-up the engine. A small base circle cam will probably be needed, and this isn't too much of a problem with a roller - which leads me into my next point...

A hydraulic flat tappet will not allow your engine to rev to 7000 rpm without a lot of unnecessary effort to drastically reduce valvetrain weight and increase valvetrain stiffness/stability. Using good components elsewhere does not warrant holding the engine back so much with a flat tappet cam, a 600+ horsepower small block Chevy should have a roller cam - no doubt about it.

Since this motor can make quite a bit of power naturally aspirated and you plan on using spray I would splay the main caps. Starting with a factory 2-bolt is great in this situation, as it allows you to do this.

The dart heads would be great. A big displacement small block revving to 7000 rpm can use a 230cc runner well.  

My bad the 3.85 should be a 3.875- good eye!