This model depicts a GWR design G27, or Loriot W. These wagons were used for carrying heavy vehicles such as cranes and excavators. British Railways also built some, coded Flatrol WW, 2/528 for the revenue fleet, and some for the engineers as well, 2/901 with vacuum through Pipes. The model requires Peco Parkside wheels, and has provision to fit the same 3D printed couplings as my BR 21t mineral wagon chassis (lifting rapido-style or NEM adapter slide-ins) although other things should be possible. Like the couplings, I have the removable girders these wagons had to help stabilise the load as a separate model. Let me know if you want them, as they're not for sale yet.
UPDATE - it all works with PD wheels and my slide-in lifting couplers (my NEM pockets would work too) but to be sure of not breaking things putting the wheels in, I had to file a groove below the pinpoint cone at the back of the
axleboxes to make enough clearance for the second end of the axle going in. Finescale wheels might be less of a
problem, or anything with shorter axles, but then you might need to fit bearing cups of some kind.
My highly experimental half-axle wheels might work too, but the filing thing works OK for me and I prefer the
Peco/PD/Romford wheels for running and weight.
I have also now uploaded the G41 version, with the lifting arm stowage box on one end platform and other detail differences including the plates at the well ends, non-DC brake levers and different floor.