Im guessing you are converting from V8 petrol to 200tdi??
If I remember right the trans tunnel and the "diaphram" bracket on the bulkhead that the front of the trans tunnel fits to are different. Using the correct tunnel also provides the hole for the gear and hi/lo CDL sticks/rubber trim. Also I think they are all bolt on. This made it easy for LR to fit different engine/gearbox combinations and use the same bulkhead/floors/seatbox.
This link shows the diaphram (td5) bracket in case you're not sure what I mean
But then again, if you are converting a 200tdi from Lt 77 to R380 Im not sure - hopefully someone with a parts manual will be able to check if the diaphram/tunnel have the same part numbers between the 2 gearboxes..............was Lt77 - 200tdi and R380 - 300tdi??
bit more digging on ebay shows a trans tunnel to be the same for V8/300tdi/td5
I also seem to remember the 200tdi is alloy whereas the V8/300/td5 is moulded plastic...........