I thought I'd update my story, with the outcome of the crazy day trip.
It all went swimmingly and after waking at 2:47, arrival at Piccadilly 4:40, the trains went as follows.
05:05 Piccadilly to London Euston. 390123. Set off one late and arrived on time at 07:27
Walk over to STP
Pint.
09:01 London St Pancras to Bruxelles Midi. 3221/3222. Set off on time, arrival about one late.
Food and coffee.
12:36 to Hassault. Br Midi to Br Nord. 75091/76071 75094/76016.
12:43 to Braine-le-Compte. Br Nord to Br Centraal. 1909/1922.
13:01 to Eupen. Br Centraal to Br Nord. 1807/1920.
13:18 to Binche. Br Nord to Br Midi. 1903.
13:38 Bruxelles Midi to Paris Nord. 1866. Six late away and held for another 10 at Noyon, but a well padded timetable had us in Paris only one down.
18:12 Paris Nord to London St Pancras. 4025/4026. Bang on time departure and 6/7 early in London.
Walk to EUS.
Food and tea.
20:33 London Euston to Piccadilly. 390125. Out on time and 3 late into Picc.
The go-for-it on this trip was the part of the journey through Mons-Quevy-Busigny-Compiegne. Nearly all new for me and an interesting way to tick it off.
Not least of which I also spotted 10 locos/36 units.
New for travel was five of the Belgian locos, the Class 75/76 units and the returning Eurostar power cars.
A long day and apart from a tiring return back to Blighty on the pretty full Eurostar, all of the trips went smoothly.
I won't be repeating the trip, as there's no need now, but I'm glad I did it, a very enjoyable day.