Can't seem to get any sense out of Ineos regarding tow hitches drop plates etc.
I don't think you ever will.
Go along to any competent trailer dealer and they should be able to sort you out with what you want.
M1 vehicles need type approved equipment, so that's the towing bracket (vertical towing interface in Ineos' parlance) and the final means of connection ~ 50mm ball, 50mm ball & pin, & NATO pintle.
The vertical towing interface is type approved ~ you photo shows the mandatory labelling.
Anything you attach to it also has to be type approved & importantly fitted in accordance with the manufacturer's fitting instructions.
50mm balls, 50mm ball & pins, & NATO pintles are all available as type approved products. Here's a type approved NATO pintle:
The only thing you have to bear in mind is to take the lowest rated value of any component into account when assessing the overall rating of the system.
So fitting a NATO pintle with a D value of 30.95kN and S value of 350kg to an Ineos vertical towing interface with a D value of 17.2kN and S value of 350kg, gets you a system rating of 17.2kN and S value of 350kg.
And then onto one of things I think Ineos has cocked up. The 50mm ball and pin offered appears to be only a 2 bolt version (4 bolt versions are available). The 2 bolt versions (to best of my knowledge) all seem to only have a S value of 250kg. Is that appropriate for a 3,500kg train weight?
The second thing Ineos have cocked up on is stating in the configurator that the the 50mm ball can fit into any of the 3 sets of holes. It can't, the hole size and spacing are both different:
N1 vehicles don't appear to need type approval for towing equipment (in the UK).
Edit: The third thing Ineos have cocked up is telling people the removeable winch will fit if the towball is fitted in the lower of the 3 settings.