Amazing, thanks for all that infomation.Your options are many and varied, but here are my preferences.
Bachmann* supply their miniature tension lock in both NEM pocket mounted and screw on versions, which is very convenient. I use both and attach by methods various:
Use the Parkside Dundas moulded screw on mounting to take the 'fishtail' of the NEM pocket;
Screw or glue on a block, and then glue on the NEM pocket, or screw attach the screw fit coupling.
It is necessary to measure for correct height, as there is no standard underfloor height in RTR or kit OO models, and if you decide to have coach diameter wheels replace the Lima wheels, obviously do that ahead of coupler fitting. There is a tension lock coupler height gauge made by 247 Developments, which is a very useful aid.
(And although not applicable in this case, old Airfix GMR design wagons have an earlier form of coupler pocket. I trim the side bars off the screw on type, make a hole in the right place for the wagon type, and install in the coupler pocket).
*I settled on the Bachmann pattern of miniature tension lock on wagons, for the simplest reasons. Firstly that each manufacturer's version is different, and by testing I determined that the two then in plentiful supply (Bachmann, Hornby) were reliable if used exclusively, but not if mixed; and secondly since Bachmann were producing most of the wagons required, I went with theirs. (Got lucky twice over because it turned out the Bachmann had a non-ferrous hook and the Brian Kirby magnetic uncoupling mod worked on them, and the variety of mountings produced is the most comprehensive.)