I may have just answered my own question by looking on the
Motorworks website (that'll teach me to Google before I post...!) - they list the housing as compatible between the following models
Fits these models:
fitsR1100GS (09/1993 - 08/1999)
fits R1100R (09/1994 - 08/2001)
fits R1100RS (09/1993 - 08/2000)
fits R1100RT (09/1994 - 08/2001)
fits R1100S (09/1997 - 08/2005)
fits R1150GS (09/1999 - 08/2003)
fits R1150GS Adv (09/2001 - 08/2005)
fits R1150R (09/2000 - 08/2006)
fits R1150R Rockster (09/2002 - 08/2005)
fits R1150RS (09/2001 - 08/2004)
fits R1150RT (09/2000 - 08/2006)
fits R1200C (09/1996 - 08/2003)
fits R1200C (09/2003 - 08/2004)
fits R1200C Ind (09/2000 - 08/2003)
fits R1200C Ind (09/2003 - 08/2004)
fits R1200C Montauk (09/2003 - 08/2004)
fits R1200CL (09/2002 - 08/2004)
fits R850C (09/1998 - 08/2000)
fits R850GS (09/1998 - 08/2000)
fits R850R (08/1994 - 08/2002)
fits R850R (09/2002 - 08/2007)
fits R850RT (09/1996 - 08/2001)
fits R850RT (09/2001 - 08/2006)