Delete Map tiles outside of map

Was trying to duplicate a large portion of my map to use as the base for the 2nd floor of my temple, and some of the items ended up getting pasted outside the borders of the map. I didn't know they were still there until I turned back on dynamic lighting and saw some torches glowing right off the edge of screen. I have no way to select them that I can tell to delete them. Any way to address this?

You can select all objects on a Layer (including ones 'off-screen') using Ctrl-A. It should then be easy to move them into view and delete them.

Ctrl-A doesn't seem to work for me, it just ends up selecting everything inside the browser window (chat, all text, etc.) Also, This map is *huge* - Worried I'm going to have a devil of a time deselecting everything else if I do manage to select every tile and prop in the layer.

Click on the Layer first, and then use Ctrl-A. Move every object slightly such that the 'off-screen' objects come into view. Select the 'off-screen' objects (e.g. by clicking on them, which will deselect the other objects) Delete the 'off-screen' objects (or move them closer to the center of the map). If desired, reposition the other objects using Ctrl-A. Hope this helps!

Followed those steps, and it worked, but now my map is out of alignment with the grid. :\ I already have dynamic lighting setup, and the map is really complex, so trying to go back and manually getting everything back into alignment is pretty daunting. 

I would use Ctrl-A to select all map elements then reposition them while holding Alt . The  Map alignment and you thread might also be of assistance, here.