Definitly start at the top. The rear main seal on these things (almost) never leaks. The engine valley is probably full of oil and draing down through the drain in the back of the valley. My HPOP O-rings were leaking not too long ago.
Sacrifice your turkey baster, get all of the oil out of the valley with that and a long pair of needle nose pliers holding shop towels. Getting all of the oil cleaned up helped me pinpoint my leak sooner. Like Logan said, get up in there with a flashlight and a mirror and look all around the HPOP. Do this while it is running.
The Ford O-ring kit (9A543) includes the (3) O-rings for the supply lines on the drivers side and the big nut on the back of the HPOP towards the firewall. The one with green or blue paint on it.
If those are replaced and it still leaks from there like mine did, there are also two more non-servicable O-rings inside the quick disconnect nuts that hold the supply lines to the HPOP. Those nuts need to be replaced if it still leaks (Ford part #9C402).
Also, check the turbo pedestal for leaks. If it is the pedestal, a good sign of that, is that the oil will only be in the back of the valley (I think).
Hope something here helps, don't let this make you go back to being a chevy guy, we'll get it, the guys on this site are awesome!