I actually think you are better off doing this as the heater core in these trucks is usally a weak link. I will rarely use my heater since my truck is a fair weather only. They sell several types (originals too $$$)I put two valves on mine since I handmade my own by tig welding a SS valve to SS nipples. My recirculating type puts out lots of heat without the fan on as well.

http://community.webshots.com/photo/2068064110102454676CppHWm
http://community.webshots.com/photo/2829150170102454676zjUUHc