My brother ran a Holley EFI on his Suburban at one time. He ended up swapping to a carburator before he sold it. He wasn't impressed with it.
The Chevy TPI system will scale to a mild 383 but has to be modified to support the kind of horsepower you are talking about. I have a TPI and am mostly happy with it, but I'm not making anywhere near that much horsepower.
