You're exactly right. I took a Dash Integration Module (DIM) out of a 2001 Bonneville, secured it in the spare tire well, and wired it into the car and created my own data bus. I also soldered in the 16-pin Data Link Connector (DLC) to allow a Tech 2 scanner to interface with the Class 2 Data bus, reprogram the radio or the DIM, etc. The DIM also converts the steering wheel control voltage to a Class 2 signal. In addition, I obtained a 12-disc CD changer from a 2001 Aurora and a CD changer harness from a 1997 Camaro and connected that to the radio, also adding the changer to the data bus, so everything communicates via Class 2 just like in a newer vehicle.
Funny you mentioned the confused GM technicians. I've had a few puzzled looks already.