Two further vans in the series constructed in-house in Douglas Works by the Railway Company and re-using the underframes from two four-wheel carriages which were subsequently mounted on bogie underframes as part of the “pairs” scheme.  Both were scrapped at some point between 1960 and 1965.  K.21 was built on the redundant underframes of four-wheel carriage B.11 and K.22 similarly re-used those of B.5.