The M.R.W.A. does not appear to have owned any bogie bolster wagons until 1956 when two old coach underframes (J12,13) were converted to N class wagons 330 and 331. Further coach conversions followed but this time the frames were shortened to 30'-0" long. In 1959 J3 and J2 became NB 335, 336 respectively followed by N337, 338 converted from J9 and JK14 in 1960. In 1964 335, 337 were reclassified Q40741, 40743 followed by 336, 338 becoming 40742, 40744 in 1965. These were all then reclassified QNS in 1966. Numbers 40743, 40744 were written off in 1975 followed by 40742 in 1985 and 40741 in 1988. The final wagon, 40745, went in 1990.

In 1962 K15 was converted to NB339 The diagram shows this as retaining its full length (42'-0") but photographic evidence shows it to have been the same length as the earlier conversions. It became Q40745 in 1965 and was reclassified QNS in 1966. Number 40745 was written off in 1990.