Thanks, aeronaut.
I purchased a retrofit kit from Incartec which included the steering wheel control adaptor. I didn't want to commit to a major new head unit purchase without trying it first so I found a used Kenwood double din stereo with Bluetooth but no screen (DPX504BT) for $60. I confirmed that the wiring is all good with a test in the car. Even the steering wheel controls worked which I was skeptical of. The plan is to try this out in the car for a while to confirm that I like it and then I can choose a newer Kenwood unit with touchscreen and all the latest tech, including back up camera, Android Auto, etc.
With the wiring all good, my problem now is how to get the unit physically installed. It seems like I have all the parts you (aeronaut) had (face plate, double din cage, etc.) but I can't see how to firmly attach the cage to the opening in the car? The opening looks identical to the pics you provided of your car. Any help would be appreciated.
Below I've included some pics showing the various parts on the workbench.
The black box on the far left is the steering wheel control adaptor. The other black box is the adaptor to reduce speaker volume (and is adjustable) as the Kenwood speaker outputs are connected to the Saab's original amp and the Kenwood pre-outs are not used. Not the best from an audiophile perspective and I questioned Incartec on this. They said this is their preferred solution for the Saab. Certainly an easier solution for me and on initial testing sounds fine. I can modify it some time later to use the pre-outs if I think that's needed.
Attachment 17516
Below are the unit and the cage.
Attachment 17517Attachment 17518Attachment 17519