Excellent work Chris!
In the past, i've used BT-FM transmitter modules where you link the phone BlueTooth to the module and the module then transmits on a frequency you chose. These were pretty successful until i bought a stereo with BT built in and then it kind of avalanched when i bought my CR-V last year and the OEM head unit was DOA.
Ended up buying a flat-screen touch-screen thing with a nice surround made for the car and GPS built in, also has BT connectivity Android Auto so displays the sat-nag from my phone on the 9" screen. It does other things from my phone as well but haven't worked those out yet!
Now bought a 7" version for my Jag to replace the OEM unit (that still works but has no screen/sat-nag built in) and i have built that into a dead used head unit using the casing to make the new touchscreen factory. It'll mean i won't have to put up with a single DIN head unit held in place with foam packing in a (slightly under) 2-DIN hole!
I appreciate none of this would look right in an older Volvo 7/9xx (might get away with it in the last 960/first V90) but it wouldn't look wildly out of place. As such it might give someone other ideas.