Yes, an R380 for a V8 can be converted to 300Tdi by changing the input shaft. It will be necessary to check and adjust the bearing preloads after swapping the input shaft. This will require completely dismantling the transmission. I have a 300Tdi R380 core out of a Discovery, however, I have not dismantled it to check the condition of the input shaft. It is completely locked up, so there's no guarantee it's good. I can strip that box down if you'd like and see if the shaft is still good or I can get a new input shaft pretty readily from the UK if you require it. Call me at the shop if you can.