why do i have to get an engineers report?

[blitzmile]

firstly i called up the epa in victoria and they told me i could fit a 2 litre pinto engine into a car so long as it was before 1976. that is a any year engine before 1976 into any year model escort before 1976. so that was fine. i then called up vic roads who told me that i need an engineers report if the engine is off a later or earlier model car. mind you this was before any emmision controls came in. my question is this why do i have to get it engineered if it of the same capacity, bolts straight in and is an almost identical match to an engine of the same year as the car?