Hello mate , we are doing a similar install on a 318 at the moment and we wanted to do the same as you and move the aircon unit down to the bottom. The problem we have is there seems to be a large plastic box/cover behind that part of the dash with what appears to be two thermometers/thermostats installed. Do you have this in yours? If so how did you get around it?
Oh, by the way, Top install!! :-)