According to the EPA it is OK to convert a different manufacturer's complete certified engine and emissions system from the same model year or newer donor vehicle. They say that this is difficult and costly to do, but it is OK as long as the rules are followed. Here is an exerpt from the US EPA "Engine Switching Fact Sheet":
"It should be noted that while EPA's policy allows engine switches as long as the resulting vehicle matches exactly to any certified configuration of the same or newer model year of the chassis, that there are some substantial practical limitations to performing such a replacement. Vehicle chassis and engine designs of one vehicle into a chassis of a different manufacturer and have it match up to a certified configuration. Therefore, practical considerations will generally limit engine switches to installation of another engine which was certified to be used in that same make and model (or a "twin" of that make and model, e.g., Pontiac Grand Am and Oldsmobile Calaise). In addition, converting a vehicle into a different certified configuration is likely to be very difficult, and the cost may be prohibitive"
All of this information is available on the EPA website.
Robert
