Got the diff sorted out whilst the tank was out but before putting the stainless tank in I needed to prep the underfloor area. The central part still has the original protection on it ion good condition so seems a waste of time removing it to just put it back on again. The outer areas had some surface corrosion so that was scraped off, kurusted and undersealed.
The photo shows where it was fresh with underseal. It also gives a good view of the rear Ron Hopkinson anti roll bar.