Are you going to be tracking the car or putting down some serious power?

Just so you know... It costs about $600-$1000 (Depending where you go) on LABOUR alone to change a clutch/flywheel on a DC5... so I can imagine labour on fitting a LSD is not going to be cheap (As you have to take the gearbox out, open the gearbox, fit the part, put the gearbox back together, put the gearbox back in).

Get a few quotes for getting a LSD fitted before you go ahead with getting it all done.