Fit the whole caboodle as a complete unit, it will be much, much easier! If changing bushes is easire off the car then now is the time to do so if you want.
Don't forget that now you have more rear end braking you may need to add more to the front to avoid the rear end locking up. The simplest way of doing this will be to fit the corresponding front brakes from the donor car or get a bigger disc kit.
I did a similar job to my Cavalier to get rear discs. Fortunately the rear beam on the Mk3 was the same size and shape as on a Mk2! I had to put the bigger front brakes on too.
See the hidden rear door handles on the new Civic: That's Honda leading the way in design...