Hi Marcus
Going off some old production line pics,the box and extension housing is grey, the same as the motor. But then again, I recall seeing them black with a silver or raw alloy extension housing and black at the very end where the tailshaft fits in.. For originality I be inclined to go with the factory pics,all grey, just in case. But knowing Holden it could of been both.Anybody else got some ideas? I've got a paint code somewhere for the grey paint,will see if I can find it for you.
Cheers
Tony