I'll stick my 2 cents in and to agree with what others have said.
Fixed back bucket seats are only legal if:
1. They are ADR approved (ie they have passed the ADR testing. Most Brides aren't to my knowledge, Sparco Pro 2000's are for example)
2. The mounting you have made in the car is signed off by an engineer. This includes aftermarket everything.
Harnesses are legal if:
1. Your car was pre 1974 (perhaps 1976?) which from memory was the year the ADR's came in for retractable seat belts. Anything after this, and you aren't allowed to wear harnesses unless you are on private road/race track or they were a factory option.
2. The harness doesn't stop or hinder passengers entering/seating in the car if there is a passenger seat in the back for example. Typically you can get away from this by removing the rear seat and getting the car registered as a two seater.
3. The harness is only a four point, and is AS (Australian Standard) tested. Klippan or RPM I know are two harnesses which comply. They must have the common style clip mechanism, and must conform to the Vicroads/RTA/QLD government dudes/etc. fitment recommendations (ie so you don't snap your back in half with your seat when you have an accident)
Fixed back seats are extremely comfortable (even doing 8 hour drives in Tasmania Targa roads on full boost with the missus as a passenger). Reversing is the only thing that I find is annoying.
I've got Sparco Pro 2000's, Klippan harnesses and a whole lot of "It's legal Mr officer" in the glove box of my Datsun 1600.