Ii mean converting a later bay kombi so that the rear valance can be removed with a few bolts to make engine removal etc easier, much like the earlier bays. The main reason the idea appeals to me is the ability to remove an engine with the car still in the garage. Most standard garages like mine (the ones integrated into the front of a house) don't have enough height to raise a van up high enough to drop a 1600 engine and pull it out. And who really wants to leave a bus parked outside on the driveway to do this.

Anyone done it? Is it worth the effort? I am sure I have heard of it but never seen any example of how it would be done? Does it form any part of the structure of the body on a late bay?

In bays it is part of the structure, so I wouldn't recommend cutting it.

Cut a lowered area into the floor of your garage, like a 30cm deep inspection pit?