DIY timing belt change

[Art b]

I'm going to have a go at this soon but have a couple of questions.

In this video

https://www.youtube.com/watch?v=0cjDDaAlEKg

He locks the bottom pulley with a drill bit through a flange with several oval holes in it and one round one, (its the flange behind the aux belt pulley) what exactly does this lock, is the flange keywayed to the crank shaft and is the bottom timing sprocket keywayed as well or are they all free to move independently once the bottom pulley bolt is removed? In a different video I watched he jammed a screwdriver between the ring gear and bell housing, that seemed quite secure.

Secondly I don't possess an air ratchet so whats the best way of loosening the bottom pulley bolt,  I was thinking a ring spanner and lump hammer. Alternatively I do have a Milwaukee impact driver with a socket attachment but I doubt its man enough to undo this bolt, it did undo some glow plugs though.

I did a 206..it was a piece of cake..
I presume their the same..