I've got the parts manual for 86 on and aside from the anti roll bar stuff there are different detachable cross members for the different diesel and petrol versions. If the detachable memner is tubular then it would seem to be a late 2.5 diesel or 3.9 petrol, square is for 2.4/3.5.
Try rangerovers.net where they give a year by year list of modifications and you might be able to make out what changed.