I've done it, but it's an easier job in a full size car than a Firebird.
If you're going to do the job yourself, the best piece of advice I could give would be to get a factory service manual. You can buy them new (reproduction) or try to get a used one on ebay.
They spell out how to do this job in fairly simple terms.
Be thankful that your car is LHD, because if it was converted, all bets are off and the job could be a far more gigantic headache.
Be prepared to spend the whole weekend doing it.