Power steering on a 2.5na - pulley question

Ok guys, i have had a search and still not clear on what i need pulley wise.

I currently have a 2.5na with a double bottom pulley, my alternator and waterpump are running off the smaller inboard pulley nearest the crank. I have on the outside a larger pulley thats doing nothing - i *think* it was for a 24v alternator that i no longer have.

I want to fit power steering, can i run my alternator off the small pulley and the power steering off the larger pulley or what?

I have seen some photos of a triple pulley with the alternator off the back, the middle pulley either redundant or running a 24v alternator then the power steering running of the next small pulley at the front.

I have also seen a double pulley setup with the alternator on one belt and the power steering on the other pulley. Which is right?

I no longer have, or will be getting a 24v alternator so have a redundant pulley doing nothing.

If my current pulley isnt right is it just a case of adding on a third pulley to the front of the crank or do i need to change all three?

Does the pulley need to be a certain diameter or is it as long as the pump and pulley line up then it will work? - i mean can i use spacers etc on the power steering pump to get it to line up?

Cheers

Ed

found a helpful answer here, Power steering fitting instruction for 2.5n/a - Page 2 - Defender Forum - LR4x4 - The Land Rover Forum looks like i need the different pulley