I am sure the Harry West Dual Spreader would be a big seller if you where to make one and probably the dump trailer too although a different manufacturer other than McCauley would be better as there aren't as big as say Kane or Marston for instance.
A Kuhn mower would be good too could maybe paint them in JD colours to go with the Britains JD mower.
My suggestions would be:
Root crop equipment like Haulm Toppers, Planters, Harvesters, Picking Tables etc.
Silaging equipment like tedders, hesston baler, bale chasers, flat and silage trailers etc.
General farm equipment like straw choppers, Quicke Loader, Pivot steer telehandler.
The list is endless believe me
Thanks
Nathan