The only place I ever saw the 6 wheel RR was in the RAF airfield fire stations.
I think they were a special build for the RAF by another contractor such as Carmichael specifically as a lightweight fire/crash tender.
There's an item in this monthg's LRO mag about a Carmichael still working somewhere.
That's all I know, I was reading it in Tesco whilst SWMBO was shopping.
thats a tacr2 or it was but i think the engine swap may be a bloody good one and there is a fair amountof tinworm in it so its got to be bought by a lover of range rovers or someone will buy it for the engine box and rolling chassis