[W126 Coupe] diff dilemma

[Divov]

After Sundays race, the need for a LS diff was so obvious.
Today's visit to the breakers yard revealed any number of W126 diffs with the ratio 2.47 which I believe (?) is the ratio used in the 560SEC.
However, none of these diffs seem to be LS units (see test below) and I took the back plate off 1 and confirmed that it was not a LS unit so presumably these units all come from the 4 door sedans.
I have it on good authority that you can identify an LS unit by the following process:

Hold the input shaft flange (prop shaft end) and rotate one of the side shaft flanges.
a) If this diff is LS; the other side flange will rotate in the same direction as the flange you are turning.
b) If the opposite side flange turns in the opposite rotation to the one you are turning, this is a standard non LS diff. 

Alternatively, 
jack the car lifting both rear wheels. (hand brake off)
Rotate 1 wheel (say in the direction to move the car forward) ;- which way does the opposite wheel rotate?
a) If it  rotates also as if to drive the car forward, the diff is an LS diff.
b) If the opposite side wheel rotates so as if to reverse the car, this is a normal non LS diff.

Can anyone confirm this test?? i.e. If you know your car has an LS unit, does it behave as described above?
What bothers me is that I did not find a single diff, from any MB model, which performed per an LS diff using the above test.
There is a diff claiming to come from a W126 500SL (with ratio of 2.24) which doesn't behave as a LS unit per the above test and surely to goodness Merc gave the SL's an LS diff??? Incidentally this "SL" diff has a totally different casing to our SEC diffs and does not have the big rear 'rubber mounting'
It also has some electrical solenoid or whatever with wires coming out of it??
The part # on the rear cover is R1263510908 & stamped on the right "ear" is 0865442   2.24
Anyone out there able to cast any light on this???????





The part # on the rear cover is 
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