The 603 is sensitive to a number of things that the 617 is not, including faulty injector lines.

If the smoking could be steam then you might have a head gasket issue which is all too common on the 3.5 engine.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.