"Hen's tooth" 1985 300D exhaust parts issue

[whunter]

Here are some photos of the exhaust system issue we ran in to. Perhaps this would be a useful tip for folks to watch for when they order this expensive part.

There has to be some way an owner can tell which pipe his vendor should get for him.
The critical dimension is 4+ inches longer from the turbo bend to the floor board bend for the later 1985 300D downpipe, conversely about 4+ inches shorter for the same one which goes onto the early 1985 300D and on the 1984.
I wonder if there was a serial number break-point for this.
Are other parts higher / lower than they ought to mate up with this?