I had my '65 Comet AM-FM repaired by Mike Hagan of Fairless Hills, PA. He's about a 20 minute ride for me, and I had known about him for many years prior to my needing his services. About 5 years ago, I drove to his house with my prized Bendix AM-FM, and dropped it off. He gave me a quick tour of his interesting shop. My radio was repaired for a flat rate, which was around $125 at that time, and it took a few weeks for completion.
He did mention that he was able to perform Stereo conversions on vintage radios without altering their fit or appearance.