Hi Mate, the other question on my mind is 
 "How hard is it to change an automatic engine to a standard flywheel type?" 
 I,ve been offered a fairly low mileage 300tdi auto engine and box at the right money(wonder if its the same one as you hve been offered?) for my 130, but I don,t think the box would be too happy pulling my loaded truck around.
I have the parts cat for defender but not for the disco to do the cross referencing.
 Gaz