Adam,
It's quite tight behind the existing radio as it is. I have a non-factory head unit, and use one of those short conversion looms to connect the factory loom to the head, and it can be a right PITA getting the head unit back into the slot. Having said that, if you do away with the big chunky LR ICE connector, and solder/crimp direct to the new head units loom, it may just fit !