One power twin set (M50446 / M50521) was converted at Doncaster Works in 1982 and became M78851 (DHBS) and M78601 (DHC). The work involved the removal of one engine and drive train from each vehicle, an an attempt to reduce running and maintenance costs. The set carried experiment number EXP DM352 in the same form as set numbers under the drivers window.
Here are details of the modifications detailed in LMR Traction Bulletin Issue 33 (February 1982):
In ex-works condition after it's conversion to a single-engined vehicle, M50521 is seen in Doncaster Works on 7/3/82. Jerry Glover.
Single Engine Conversion
3-car diagrams & Works Pics
2-car diagrams & Drivers Instructions
4-car diagrams & Works Pics
Details about preserved Class 104s can be found here.
Many thanks to Kevin Dowd for his assistance in the preparation of these pages, and to Eddie Knorn for further data.