Junkyard treasure 360 efi?

If you aren't planning to take the whole engine, I'd skip it. The Magnum EFI is not easy to adapt to other engines, particularly the crank trigger setup unless you happen to have a milling machine. It is possible to reflash the factory ECUs, but be prepared to pay up the wazoo - and good luck finding someone who's actually tuned one installed on a big block. You'd be better off either trying to grab a bunch of unrelated junkyard components and run them with an aftermarket ECU, or try adapting a GM TPI computer (which is hackable if you know what you're doing, and can be made to work with Lean Burn distributors).