The factory-original tyre placard on the driver's door pillar of my 6.9 states maximum load rating 1610 lbs, which is 730kg or load rating 97.
The current-day Michelin XWX 215/70VR14 is rated at 92W (630kg/tyre) and the 215/70VR15 at 90W (600kg/tyre). See PneusCollection_broch2015_GB.pdf at
http://www.michelinclassic.com/en/Classic-Tyre-range
The permissible total weight for the 116.036 (450SEL6.9) is 2420kg which averages 605kg/tyre so the 14" XWX @ 630kg as above passes.
Even over the front axle where the max. permissible load is 1245kg or 622.5kg per side at the front, the 14" XWX passes.
I do not have information as to whether Michelin de-rated the XWX at some stage in the past from 97 to 92-14"/90-15".
A letter from Daimler might address the conflict between the 40 year-old placard and the mathematics as presented above to the satisfaction of Australian roads authorities and/or insurers.
For originality I would prefer the Michelin XWX. It also passes the common sense test. I hope Australian roads authorities see the sense in this too.