Bingo Dave - that's my understanding of the reason for the change also. Brit - you'd have to find one first. They were only fitted to very early suds, maybe the first year or so of production? Better to solid mount your existing tail extension.
Re the belt covers - I have had a stone flick up and drop down the front of the engine landing on the bottom run of the rh belt (engine idling). It then travelled along with the belt until jamming in the pulley and breaking the belt. As it happened, this was with the covers fitted (don't ask how this could come about, but it did), but with no covers it just seems it would be too easy for this to happen. Given there's only 3 screws and less than a minute to get each cover off, I can't see the reasoning for not having them on.