I didn't read this close enough the first time around. Do you have a picture of the adapter? I'd love to see it.I have been looking for a way to print the dome light lense for older cars - I need one, and whatever I learn from that I could learn to print one for my XR4Ti. I haven't had great success with transparent filament, so my next approach is going to be trying to print a bracket that can use a transparent "window" cut from stock, or an adapter that could use a lens from another car.
I got my 3D printer imagining all the car stuff I could do with it, but so far it hasn't done all that much good. I did print a pair of "compound" hub adapters that center both a too-big brake rotor and too-big wheel that works excellently. That solution save a pile of cash!
Have you considered printing a new bezel that could hold either a flat plastic disc or the dome lense from another car that is close to the Saab part? I'd be willing to tackle the design if you can supply an original dome light assembly. I'd send it back to you after I capture the critical dimensions.