I'm betting everything including the HVAC programmer are different. And remember the ECC gets it'* VF display control from the HU of the stock stereo. And doesn't use manual valving at all.
Anyone recall how hard it is to get to the programmer?
You wanna see a car torn down, that'* the time to see it.
The other problem is that after you get it all hooked up, and it doesn't work, it'll have the flashing temp display. Then off to the dealer you go, trying to get the codes read.
I'd suggest if you're going to try this, use the 92/93 ECC so you can use the built in OBD if necessary. But you'll still probably have to swap Programmers, too. Among other stuff including alot of wiring.