393 or 408 with 76mm turbo

If it's gonna take all your money to get it done, why not do it in stages instead of doing it twice.
Skip the turbo for now, and do the shortblock, better heads, cam, and intake first.
With a 408 and no turbo with good h/c/i it should run mid 10's anyway.

Building anything twice sucks and is always more expensive in the long run.

You don't give enough detail. Why are you going with a 76mm turbo? Is it one you already have? If so, which 76mm turbo is it? Precision makes a GT42 based 76 and a 76GTS. What frame are you using and what is the hot-side A/R? Pretty much at 76mm turbo is going to be a quick spooler on a big Windsor. If you don't go big enough on the A/R you're going to choke the hell out of the motor. If I had to run a precision 76 on a big windsor, I'd personally go with a GT4276 with a T6 frame and a 1.28 or larger A/R.

As far as what it will dyno, it's up to you. I've seen a GT42-76 make 850ish rwhp through a TH400 and over 1000 rwhp through a T56, but these were both on smaller motors where this particular turbo is more efficient and not as choked on the exhaust as yours will likely be. You won't be able to do this with stock internals, either. The car with the TH400 went 8.76@15X mph. So if you want to run 10.0.... no problem

Chris