Crankshaft oil seal help

This could be the first of a few questions during my engine rebuild, so I apologise if any are daft or become annoying!! 

Firstly does the oil seal sit flush against the external wall of the plate (see pics) or does it sit flush against the internal lip?!

And secondly, is there only one seal for the plate as included in my bottom end gasket set is a large o-ring that would fit perfectly inside the plate (again apologies for the daft question - it was four years since I stripped the engine!!) 
Many thanks!!