you are swapping from drums to discs, I have never made that swap myself. Here is a link that should help:
I know the above can be a bit confusing because Subaru mixed and matched their rotors and calipers quite a bit. The 266x10mm solid ROTOR has been used on most of the rear disc equipped Subarus made since 1990. The single pot caliper used to squeeze this rotor has changed. The (1990 to 1999 Legacys and OBs) and (mid-1998 and older Imprezas and Foresters) seem to use the "older" style single pot caliper and bracket. Mid-1998+ Imprezas and Foresters and 2000+ Legacys and OBs use the "newer" style single pot caliper and bracket. It is the "newer" style caliper used with the 2000+ Legacy caliper bracket that yields the 290x10mm upgrade on WRXs, earlier Legacys, etc.
The older calipers are not compatible with the newer brackets and vice versa. So if you source the older calipers you cant use them for the 290x10mm(H6) upgrade.
Read this link for pics of older and newer style single pot rears. http://forums.nasioc.com/forums/show...hreadid=234120