The plan was to introduce the new casting with the drainplug at the side for the upcoming 3.2 enginge. Though, the moulds for the casing halves (old 3.0) was so worn in medio 83 that it was decided to abandon them, and start Production of the new castings in the new moulds at the end of the 3.0 era.
So what you have is one of the very late 3.0 litre engines
