From DRB's web site FAQ's
In many overseas countries GT40's are registered as 1968 or 1969 model cars and therefore are not required to have EFI motors, catalytic converters etc. In Australia, replica's are registered as new vehicles and must comply with about 75 ADR's (Australian Design Rules) as well as each State Transport Dept's regulations, the most important issues being exhaust emission standards and chassis strength. Some States allow motors up to 5 years old to be used (ADR 37.01 compliant) - 1999 or later. In these States, the Ford 5 litre Windsor can be used, or alternatively, the Ford Mustang 4.6 litre alloy Quad Cam motor can also be used. Other states require motors that comply with the current emission standard (ADR 79.00) 2003 or later. In this case the chassis is modified to allow the Ford Boss 5.4 litre Quad Cam motor to be fitted.