Having used SUPERFLEX myself, this was my view about the bsuhes, all are ok apart from the beam bushes, seriously too hard, was taking me poor little xr4i a load of power to try to drive through the vibration.
You might as wel try and save a bit with your local and try SUPER PRO, they are made in your country after all.
My sapphy has poly beam bushes that were on it when purchased and they are not too hard, not sure of make though 99% sure it is deflex, or floflex as they are called now.
I don't think many peeps tried the GGR axle tightening kit as it seems expensive for 4 bits of nylon, but certainly when I used it, it worked brilliantly, with escort cossie beam bushes.
Even with poly on the arms etc, the up down movement of the diff will take place, so yes still defo need the poly diff mount.
tabetha