finally it looks like V-8 time

You could easily (and cheaply) build a 300+ HP 318 with mildly ported 302's, a good cam, Performer or similar dual-plane and 600 cfm carb. A complete EFI Magnum engine does sound attractive but IMO that "beer-barrel" intake is giving up a lot of higher-end power (kinda like the old longhorn cross-ram BB intakes). There is a dual- or single-plane intake by Mopar Performance that has injector bungs(?) cast in, so you could swap one of those intakes on a good junkyard Magnum engine and you'd have a pretty powerful engine.