How do I snap one object into place with the opening of another object? (See picture) As you can see, I'm trying to put this object into the opening below it. Is there a quick and easy way to do this? The top model is not rotated exactly correctly to match the opening, although the model is exactly the right size so if it were matching orientation it would fit. I'm looking for a way that I can sort of 'click' the top one into it and it will adjust accordingly.
If it's only about location and rotation around the Z axis, it should be as simple as:


Select the object you wanna align
Go to Editmode Tab
Select all A
Make sure you are in Vertex Select mode CtrlTab
Hold Shift and click a vertex twice, which you wanna use to align location(makes it the active vertex)
Enable Snapping ShiftTab
Make it snap to vertices CtrlShiftTab
Set Snap Target to Active
Grab your object G and snap it to the other model's corresponding vetex
Snap Cursor to Active ShiftS
Change Pivot Point to 3D Cursor .
Hold Shift and click a vertex twice, which you wanna use to lineup rotation(make it active)
Rotate the model R, constrain to Z axis and snap your vertex to the corresponding vertex of the other model(this can be really tricky, try to make the models a bit transparent to see what you are snapping to)


Not sure if the vertex in step 12 needs to have the same Z location as the first vertex... But even then, it should be possible to use any vertex with a bit more effort, to be able to constrain the right rotation axis in step 13 - using a custom transform orientation, which you would have to set up first...

If the models did not align originally, you might be able to snap to edge instead in step 13...