Been doing a little more research into this and I'm not sure the mk2 RS setup will work?
we already know that mondeo mk3 calipers will fit the sierra hub and all mk3 mondies have the same brakes as far as I know?. A popular bolt on upgrade for st220 is the mk2 focus st setup so therefore these should also fit the sierra hub
however the mk2 RS brakes are apparently not a bolt on upgrade to the ST cars due to the hub carrier being different.
i wonder if the mk2 ST calipers will fit over a MK1 RS disc? 320x25mm vs 324x28mm??