if you have the time and access its well worth replaceing them with polybushes,it tightens up the rear end nicely and seeing as you are doing the beam it would be a shame not to do the trailing arms as well.
the poly bushes in the trailing arms are simple to install but to remove the standard ford ones can be an ordeal,for a start you will need to press the old ones out and they can be very tight so if you know someone with a hydraulic press all the better.