Box section door, do you mean the early door?
You can see in my photo of an early door that a td5 catch fits but the diameter of the key barrel housing won't fit in the hole in the door with the bezel fitted. This might suggest the key barrel is bigger on a td5 and later.
Sorry I don't know the part number or key hole type/size.Rear End Door Latch Mechanism - Find Land Rover parts at LR Workshop
View the Land Rover parts diagram for Rear End Door Latch Mechanismwww.lrworkshop.com
What is wrong with your original catch?
You can get repair kits on Ebay, I had a spare TD5 one so used that until we repair the original one, eventually.