Just to follow up on this - I had to do two 'fixes' to get this so I was happy with it.
Firstly was to slightly shim the subframe mounts to get it to line up with the front.
Now the front and back subframes line up all nice.
https://i.imgur.com/43OjE1b.jpg
Also the drivers-side of the floor wasn't side enough for the boot floor + both little infil panels - it was about 8mm too thin. I had to open up the corner, and pull the outer sill out a little, then weld the box-ish corner back up.
https://i.imgur.com/5gQAKZJ.jpg
https://i.imgur.com/mWTFvqn.jpg
https://i.imgur.com/8mlNNou.jpg
https://i.imgur.com/Kv0hH1R.jpg
Anyway - annoying but now sorted. Thanks for the help/etc. :)
Edited by AlexB, 29 December 2023 - 06:09 PM.