Q: I'm putting in a police interceptor motor from a Impala to a 2005 Monte Carlo but it has fly by wire

Prior to doing this work, you should confirm that the "new" vehicle configuration is certifiable insofar as Federal emissions law, that is if you intend to register the vehicle. Please see the relevant Federal EPA Engine Swap Guidance Document. California, and a few other jurisdictions, have additional requirements and, in the case of California, these are published in the California Engine Change Guidelines. Unless you have very sophisticated test equipment and a thorough understanding of what is allowed in an engine swap, you are much better off keeping the stock (original) engine and, if need be, simply rebuilding it. Indeed, that is the advice stated up front in the California guidelines document. Assuming that the swap will be certifiable, or to even get to the point where you can demo it for certification, the computer that runs the donor engine, along with most of the vehicle wiring harness for that engine will have to carried over to the recipient car. Unless the engine weight is identical, any alteration in weight will require suspension and alignment modifications that will have to be engineered. If you are interested in an engine replacement (stock OEM to OEM), or rebuilding services on an existing engine, YourMechanic professionals in certain locales can assist with that. Please simply inquire based on your locale. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.