In 1960/1961, ninety six large steel boxvans were built and placed into service. The class numbers were 23 to 118. The body design was similar to early style VLX_, except pressed sheetmetal was used for the sides instead of louvred sections.
In 1961/1962, the class was modified and relettered to _BF_ or BLF_. In early October 1961, ten vehicles, 35, 41, 45, 54, 57, 75, 85, 88, 93, 105, were modified to _BF_. From late October 1961, the class letters BF were altered to BLF. All remaining conversions from BB were to BLF.