I've got a '75 Jimmy with a 400 in it. The engine is REALLY tired, with about 230K on it. I bought a fuel injection setup off a friend, who had it on a '57 Chevy w/ a 400 (he replaced it w/ a big block). Do you guys think I should rebuild my existing motor, or get a crate 350 or 383? I'm worried about the setup on the FI computer. It was setup for the 400, so will different CI screw it up?