I would imagine that a lot has to do with availability of a donor car for the parts. It certainly can't be worth it to buy all the required parts "over the counter". But with a good donor car, it's certainly "do-able" -- lots of guys on this list have reported doing so successfully, so if you've got the donor's parts, go for it.

One other thing -- you didn't mention what years your car, and the donor car, are. There is also at least one critical transition period (there might also be more) in which you cannot cross between donor and recipient without a LOT of extra work and parts -- I'm referring to the '85-86 period, in which there's a change from mechanical (cable) driven speedometer off the transmission to an electrically driven speedometer with signals from the differential.

Good luck.