Although not a 4mm modeller, I know several who do model the GE in the various 4mm disciplines, and who would, I'm sure, bite your arm off for some decent wagons. I think the way I'd go about it would be to etch the standard GE underframe (incorporating fold-down axleguards, vee hanger and central cross-shaft support, with the brake lever, brake guard (alternative versions) and optional Monarch balance gear all on the fret), and resin cast the bodies (worth reading the article by Maurice Hopper in MRJ 199) - except of course for the dia.16 open which would also have resin solebars/headstocks. In this way you would be set up for a wide variety of wagons without having to reinvent the wheel each time.
Interesting to hear about Widford. I used to play in the remains of Hadham amongst the rubble and gutted box once the coal merchant had finally quit the yard - my grandparents lived a stone's throw from the site. Later I used to walk the dog from Standon north up the line to Braughing or south towards Hadham, always on the lookout for bits I could retrieve. One of the Standon down signal posts came down in a storm in the late 80s, but that was too big and heavy to drag home... but I did manage to retrieve an 1879 GER 2-hole bullhead chair from the formation just south of the bridge at Widford which props open my workshop door.
So I'd certainly be interested in any artwork you produce for the Widford buildings which could be shot up to 7mm. As my local line, and despite my current East London project, the Bunt has always been my first interest and Widford was as photogenic as you could get. Somewhere I have plans of the early GER 10' x 10' signal cabins which in the early 1890s were converted to waiting sheds on the Bunt stations - if you're interested I'll see if I can dig them out.