The 4.6 connecting rods should say HRC2382 on them and the 4.0 will have HRC 3283. I'm not sure about the pistons, but can post a photo of a 4.6 one if you'd like.

 

HRC 2383 is what is cast into the connecting rod.
do you happen to have a clean 4.6 piston to photo? that would be great, thanks.
also the block is 56Dxxxxx... so a 4.0 if the chart I'm reading is correct

 

2383 is a 4.0 connecting rod at least according to this ebay listing.
https://www.ebay.com/itm/201754527587

I dont have any photos of the clean face with the markings, but I do have a side view. But even the same pistons have different markings. I think one said J5 and another M6.

Both pistons looks very similar on the photos from British Atlantic. But I think the 4.6 one has a deeper dish.
https://www.roverparts.com/engine/pi...rings/ERR5553/
https://www.roverparts.com/engine/pi...rings/ERR5554/

 

It looks like the 4.6 Piston may be a little taller as well, but if the connecting rod is for 4.0, there is no way it has 4.6 pistons on it.