A chap from the GNSRA has commissioned a set of CAD masters, initially for his own HO layout but also available scaled up to 4mm. I have requested a set and will report in due course. They are only a sides and ends resin casting but that takes a lot of the legwork out of building something. Mick is looking into buffers and axleboxes, I believe. Available diagrams are:
14s 8 ton with wooden underframe
15S 10 ton with steel underframe
later 15S with steel underframe and end with louvres and drop panel
16S 10 ton with wooden underframe and end with louvres and drop panel.
The built examples above have been made up using proprietary underframes. To be more accurate the headstock was channel with the buffers mounted on wood packers, the spring trunnions are very distinctive and the steel and wooden underframed bodies had slight differences. Photos in Tatlow, on the Cheona LNER wagons book and in a booklet available from the GNSRA.
These castings are available though http://www.chrisjward.co.uk/ although there is no information on there at present. I'm awaiting confirmation of the price although I'm advised it is 'in the region of £10'.
PM me for further information if this doesn't answer any queries.