I agree with Benzmac. The old systems were problematic and the difference in displacement would be difficult to overcome. I've had good result with Electromotives Systems. Although this will require lots of R&D the end result could be a car that out performs the original. The original mechanical injection on the 6.3s was full of compremises. One other logical replacement would be to adapt K'jet from a late 70s 6.9. Its sounds like fun to me!