OK,
yes the hole above the oil drain is the oil feed supply. The one towards the rear is the water feed, the bigger one with the flat face (because you use a banjo fitting with a copper washer to seal) . The water returns behind the block and into the block via the one of the big bungs on the other side of the motor in your second picture????
The lower hole on the right just has a bung in it and it's a factory water drain plug.
I assume with the wastegate, presumably the bottom hole has a pressure feed to it which regulates boost. Get a feed from the plenum inlet. Boost will be regulated by the spring rate. ie with a 15psi spring, with just a feed to the bottom you will get 15psi. However if you want more, you need a boost controller/regulator, which feeds normal pressure to the bottom and regulates how much pressure to apply to the top hat which equalizes hence regulating a higher boost level.
Hope this helps.
Cheers.