The original Aquarius conversion was Piazza rotors and emergency brake, that bolt right onto the Gemini axle. But there seemed to be an extermination program against Piazzas in Australia, and the remaining 100 or so are fiercely protected by the members of the Australian Piazza owners club.
The emergency brake rides on the inside of disk and is a mini drum brake, so there are three braking surfaces. Without a Piazza donor, you're looking at very expensive machine work for merely stock performance level.
You could go the exotic car route with the Brembo disk type emergency brake caliper and do away with the center mini drum brake. Only 1500 USD per pair of those calipers. Whenever people ask why you have two rear brake calipers on each side, you could say the car has the same emergency brake as a Lamborghini, Ferrari, or upper range Lotus.