I used a hot side from BG and made my own cold side. A GOOD bandsaw is a must. I didn't have a welder so I marked and taped (blue painters tape) all my joints and trucked them to a buddy. Having a welder or simply the means to just tack weld would have been so much better.
From my little experience it would be no problem building a kit from scratch.
Dart 348ci, Ed Curtis cam/valvetrain, Precision 76mm, Holley Dominator EFI, CNP ignition, tons of Holler EFI small parts, 4"dp, 4R70W w/T-brake, new suspension coming soon.
Little 750rwhp at 6,000rpms and only 10lbs of boost before we just got tired of playing with clutches. New 4R70W and we are turning it up. Expecting 1,000rwhp.