Each chassis was constructed at the Brislington Works of Bristol Commercial Vehicles, then taken by road the short distance to Brislington station on the North Somerset branch. There the chassis assembly was completed, and temporary cabs were fitted at each end, with a gang-plank and handrail adjoining them. One of them was tested on Sunday 13th April ('58) and the other each night of the following week, from 22:30 to 02:00, after the last train on the branch had cleared, and again on Sunday 20th.
The testing was carried out between Brislington and Marsh Jct., and Brislington and Pensford, requiring Pensford signal box to be kept open for tablet purposes. Although a BR driver and inspector rode on them they were driven by BCV employees.
The first image shows a chassis on test. They were nicknamed "Prairie Schooner". Picture from a contemporary Bristol Commercial Vehicles “Bristol Gazette” magazine.
The chassis were then conveyed by road to Lowestoft by BRS (Pickfords) Ltd., and off-loaded by mobile crane in the Eastern Coach Works yard where the pre-assembled bodies were lowered on by jacks and secured. The completed railbuses were then moved out over a temporary rail link laid onto the adjacent Great Eastern Line.
The first of these three images shows Sc79958 exiting the Eastern Coach Works. Next, stabled outside the Eastern Coach Works (Phil Trotter Collection). Finally, Sc79958 at an unknown location, but the Class 31 loco behind suggests it's somewhere on the ER.
The first vehicle, Sc79958, was on show at Marylebone on Thursday 14th Aug '58 for members of the technical press.