Im sure Xsport racing in Basingstoke still sell X-pack kits

http://www.xsportracing.com/ford-escort-mk2.3003304.cms

I bought 2 kits from them in the 80's when they were "Autocross"

Personally though I would keep the bodywork original on your RS, they are a bugger to get to fit right, and take lots of time in blocking out the filler work and that's after you have cut an welded your arches