i have dc rear disc on my rex. its a bolt on process, you have two ways of doing this
1. using complete trailing arm(minus what estorvito said, you will use your existing wishbone thingies..lol..) or
2. unbolt spindles from your trailing arm and replace with integra spindles
either way envolves roughly the same amount of work.. be sure to have 90-91 crx Si e brake cable's, your drum e brake cable will not fit