Think I have found the answer to my question. Searched earlier and didn’t find this. However, with more effort, here is what I found in another forum.
“the Defender V8 R380 and both Discovery and Defender 300Tdi R380 are geared the same. 1st and 5th are different on Discovery V8 R380s. If you put a 300 Tdi input shaft into your Defender V8 R380, you will have converted it. It is the only change necessary. I would not recommend running the V8 input shaft behind a 300Tdi. The input shaft is about 0.25" shorter and the pilot size on the V8 is 0.750" while the pilot on the Tdi shaft is 0.875". It would physically bolt up, but the input shaft would be unsupported in the back of the crankshaft and the clutch splines would also not be fully supported. It will not live long this way. If you're converting to a 300Tdi, it is money well spent to convert the transmission, too.“