These coaches featured flat ends and wider flanking quarterlights than the first style of Collett coaches. They were built to two diagrams with virtually identical side profiles and with the same underframes. The main difference seems to have been in the method of roof construction in that C66 had transverse ribbing whereas C75 had longitudinal rainstrips. There was also a 1″ difference in width (9’0″ vs 8’11”).
Seven C66 were rebuilt 1953-54 to diagram A41 autocoaches, as were 11 C75 to diagram A42.