Are you talking about going from digital hvac to non-digtal but still dual climate? Or are you wanting to take an hvac unit from a 99-02 model with the 3 knobs and swap into yours?
I am in the process of doing some heavy research into doing the swap from non-dual climate (99-02) and converting to the non-digital dual climate. The outcome i am looking to have is that you will be able to upgrade to the manual slider dual climate hvac, yet utilize only the single blend door on the 99-02 trucks. It will be like going from luxury to base in functionality, yet having the upgraded looks of a newer hvac unit.
First off i can tell you for sure that the 03-07 hvac units are a tad smaller in width than the 99-02's, meaning that modification will need to be made on the 99-02 1.5din bucket. If you're looking to swap the unit from a 99-02 into an 03-07, the older unit will be too wide and wont be able to clip into factory location unless modification is made to the bucket as well.
Ill keep posted in upcoming months once i get around to messing with systems.