I was having a look at Turners web site and noticed something about the new improved heads that some people have said are better than the original heads as there is an extra water gallery.
According to this note from Turners themselves ,they say it adds no extra cooling benefit.

NOTE: Land Rover 300TDI engines do not have the additional waterway facility in the block casting corresponding with the extra waterway in this later cylinder head type. Whilst an option this additional water way serves no useful purpose on the land rover 300TDI and offers no additional cooling with this type of block.