The Kenwood model is an 8017.
As far as the vent modification. It definately would be easier to modify the vent than disable the heater. The issue is not with the heater. The issue is SPACE need to fit a double din. Thus, if you want to install a double din the IHKA housing must be modified. The biggest trick is planning and patientce.
The arm controlls the opening and closing of the floor vents. I suppose it would be possible to fabricate a new arm except the vents do not have the clearence for opening and closing once the IHKA hossing is modified. Therefore you will nedd to make a decesion on what to do with the floor vents. Whatever decision you make, remove the arm from both ends to minimize problem in the future.