Looks like I was wrong about the 560SE, its the same as the 500.
So the 500 and 560SE have the shorter wheelbase, but the 560 also has a higher ride hight.
260/300/420 have the normal wheelbase
but 500 and 560 have the 5mm shorter one.
I'll have to get out the brochure collection to see if the LWB cars are the same.
This all came about because I was looking for the width of the rear seat in SWB W126's so I can work out the max width of childseats to accommodate 3.