I'd get the one you have now rebuilt; it's already seasoned, any core shifting is done.
This is with the caveat that you get it sonically tested before you start having it built. And that your machine shop has the proper torque plates for it.
But if you must go crate motor, I'd check places like Jegs, Summit, Hughes, etc. to find one that's "built" already.
Other than that, locate you a good tuner (I haven't used one, so I don't know, but I rather like how Ryan Hogan sounds in his forum; but again, no experience with his tunes personally.)
Talk to them, see what they recommend for your end goal.