Yesterday my parts came in and I put her back together. It went surprisingly well. Turns out a new Oil Trap (this is what Volvo calls what we've been calling the Oil Filter Housing) comes with a brand new oil filter already installed.
New in the box.
After I got it back together it took a few moments of cranking for the fuel pressure to build and then she fired right up. The "Running Lean" code I had before is gone now and hasn't come back in 100 miles of driving.
Here's a "gotcha" though: There are two holes on the front of the oil trap. One's for mounting the oil dipstick and the other is for holding a wire loom clamp. They're not threaded! The screws are self-tapping! That seems a little odd to me. And it's a little bit of a pain getting them started when the unit is in the car already. So it may be wise to tap those holes with the unit out of the car. Also, if you've taken them out and didn't label them the long one is for the dipstick and the short one is for the cable clamp.
Also, for tightening torques "Snug" actually means:
Intake Manifold, upper, plastic: 10Nm (7ft-lbs)
Intake Manifold, lower, aluminum: 19Nm (14ft-lbs)
Oil Trap: 16Nm (12ft-lbs)
Oil Plug: 38Nm (28ft-lbs)
If I were to do this again I wouldn't take the intake manifold off. If you can get the airbox out without dropping the radiator then good - do that. But if not I think there is enough room to do the work with the airbox pushed as far to the driver's side as possible. Working room would be restricted. But it's only 6 bolts, two hoses and one electrical connector.