If your car is late 97 on it will have the two outer hoop stanchions welded in place, you can check this by removing the plastic turrets, if there is a tube directly underneath, then you have the ability to fit roll hoops. If not then as vintage says, these will have to be welded in, you could possibly get them cut out the donor car.
If you do have them, then great, but you will need the inner stanchions, which are black bolt in items, you will also need all the plastic trim from the back as well including any brackets and screws, as the roll hoop storage box is smaller, if you have this included in your £150 then bargain.