help designing engine for turbo

When it comes to designing an engine, I can figure that out. I can even probably cobble together a turbo on an existing engine. But in my case, I'll be starting from a bare block 302w and building an engine for a turbo (or two) and I don't know just how to choose things like head flow and cams.

For instance, if I were building a 400-hp 302 I would choose a cam with about 240 degrees intake duration and heads that flow about 250 cfms intake. If I wanted to turn that engine into a 600-horse engine, I could slap about 8 psi on it. But, if I'm designing it from the ground up to be a 600-horse turboed engine, would I change anything? Should I make it easier to get air in by using larger intake ports? Increase cam duration? Or should I just let the pressure do the work?

I guess what I'm saying is; should I build a 400-horse engine with a wide LSA cam and give it 8 psi, or should I build a 600 horse-potential engine with a 400-horse cam, then 8 psi.

IMO, first order of importance is--Port the heads aggressivly. Big valves.
Then; Shortish duration, high lift cam.
Maybe 8 to 8.5 on the CR.
The icing on the cake-- Should shoot for 1 throttle butterfly per cylinder if your budget can stand it. Try to tune the intake for best torque in off boost conditions. A custom fuel injection system is probably mandatory at this level. On the exhaust, maybe tri-Y headers. You'll never get an optimum exhaust on an dual plane crank unless you cross over to equalize pulses. Mind you, this is fancy stuff-- but it works, and works very well indeed on a turbo engine.
In short, don't try to throw a lot of boost at a restrictive intake and cam. The results will be mediocre. It is borderline problematic that an intercooler would be worth it with only 8 PSI boost. You'd have to run the numbers.
Since the amount of boost showing on the guage is basically a measure of back pressure in the intake manifold, then; 8 PSI boost in a free flowing engine will get you lots more power than 8 lbs. in a restrictive engine.

Just my .02 cents worth.

IMO, first order of importance is--Port the heads aggressivly.

the exhaust valves aggressively. If you were going for a n/a setup, then I would hog both the intake and exhaust ports aggressively. Different porting works better for different applications.