The first Sierra's were 3DR (This is all the Cosworth shell is based on) no 3DR had 4x4 so none had MT75.

I can't help you in telling you if the engine would fit in or not, at a guess I would say it would fit faily easily as there was V6 Sierras such as the 2.3 and the XR4I was a 2.8 V6, alot of people also fit the 24V BOB/BOA into them.

The MT75 box I know will cope as this is the same as the XR4x4 and the Cos 4x4 not sure on the driveshafts.

Martin