Mine's a late model engine so it's the one with the two plastic rollers at the same height, immediately under the cam sprockets, with the tensioner located lower down next to the water pump.
One roller is slightly larger than the other one. I'm not sure which side the larger one is meant to go on, I was positive the larger one goes on the inlet side, until I went to Vaux this morning for two new rollers, and the blasted EPC showed the larger pulley on the exhaust side!!
If someone can just put my mind at rest, I'd be grateful. Also one pulley faces outwards with the lip away from the engine and the other with the lip facing towards the engine. My Haynes manual only shows vague pictures of the early engine.