[425HP409]

You can, although there is a clearance issue with the heater to defroster ducting. This makes the AC unit stick out too far from the dash. Back in the day,,, the AC manufacturers made a replacement defrost duct to replace the original one which allowed the unit fit flush to the firewall. I have one that was installed on my Dad's truck when he added under dash AC. I can send you pictures of it tomorrow if you pm me your email. I will also post them on the forum for all the other members to see. I have talked to Old Air Products about reproducing them, but have had no response from them. This would be a great product for anyone wanting to keep their original heater and defroster unit and add AC under the dash. If anyone out there is in the manufacturing business, I could let you copy mine to reproduce.

I have attached photos of the original defroster duct with the replacement one that was installed on my truck when the underdash unit was installed. It was one of those that just fit under the radio, not one that had the evaporator over by the passenger and the long plenum to the center of the dash.