I've got C&BT Shops kit R700, with 6' plug door,Tim and Others,
Here's the "key" to the C&BT versions: A,B,C,D,E all represent SFRD
classes with similar body styles, a "1" suffix denotes the body style
modernized, typically with six foot sliding doors.
A Classes Rr-19, 23, 24, 25, 27, 28, 32
B Classes Rr-33, 34
C Classes Rr-35, 36, 39, 40
D Class Rr-43
E Classes Rr-45, 46
Thus a C1 is an Rr-35, 36, 39 or 40 after modernization with six foot
sliding doors and electric fans. I hope this helps.