Rotating the prop 180 degrees will make no difference, and neither would rotating it any number of degrees at one end or both. The only important thing is that the two ends are 'in phase' - when the centrelines of the two joined shafts are parallel to each other. I know nothing of Discos and RRs, and only a little about Series, but 90/110's rear diff input shaft is horizontal at rest on a car with standard suspension, so should have an in phase propshaft to the equally horizontal transfer box shaft. The front axle has the diff pointing uphill (partly due to the propshaft being short) and so the front propshaft should not be 'in phase'. I didn't know that when I had my first encounter with a front propshaft, and having separated it and then finding no alignment marks had to get under other LRs to compare and adjust it. It might have been helpful if I'd written down the number of teeth or degrees - but I didn't. You might need to do the same, but it's not hard - one tooth on the spline is very obvious at the ends.
