A recent discussion of radios in a B12 on the Lancia Club site brought to mid the restoration of the radio for the 1952 B20. It was a vintage Autovox, model RA15L, a rather heavyweight from the time. Its restoration was interesting: first, three vintage radio restorers in the US wouldn't touch it. Finally found a vintage radio buff in Trieste willing to take it on! Not so easy these old parts!
He had to hunt hard, but found a power diagram somewhere, and a power source on Ebay, then proceeded to rebuild in detail. He wrote up his work: https://www.depoi.net/en/2017/restoration-autovox-car-radio-lancia-aurelia-b20