i think i just worked it out
the distance between the engine mounting points has to be the same for all the cars (sierras and granadas and scorpios) because they all have the common engine installed.
But as said earlier theres a difference between gearbox input shaft lengths and flywheel thicknesses... suggesting that some of the variants were mounted further forward or backward because of ancilleries and heads etc... could this be - just a varying degree of angle on the arms, making them no wider at all when on the car but, indeed longer when measured in length with a ruler???
or am i talkin out of my gluteous maximus?