There were at least two Juniors that left the factory as artic tractors and others were converted, I remember Hills of Botley ran one. The chassis, rear bogie, gearbox and 2 speed transfer box were essentially the same as the 6x6 Constructor so it was a robust bit of kit just lacking the extra driven axle and extra power of its sibling.
As for trailers they were often seen dragging the 60 ton (payload) Crane float trailers around with various loads including boilers and engine tenders, the video shows an unusual trailer which is the carrier from the old 100tonner fitted with a crude front bogie: