Thank you both for the replies!

I feared that the Becker modification would not use the existing microphone. They used to have more information on their web site, but I recall that they wired it through the tape deck. That would exclude use of the microphone without further effort. I'd think that this should be possible, but there may not be enough market demand to justify the effort.

Again, I've never had a call where the caller used Bluetooth that sounded good at all. Maybe they do exist, but I've not heard it personally. And a lot of friends and colleagues use Bluetooth connections in their cars.

If the Becker modification does not work (I will send them an email message), would a third-party radio be able to do what I seek? Or should I give up and start over completely?