It doesn't take much to power this project–he managed to pull it off with a Raspberry Pi Zero. For output, he uses a Pirate Radio kit from Pimoroni which includes a 5W speaker and an audio driver board known as pHAT Beat.
Michael wanted to use as much of the original hardware as possible--not just the outer shell but buttons and knobs, too. This proved to be a challenge, so he opted to order replacement components of the same size. Some 3D-printed structural pieces were necessary to help hold the electronics in place.
As far as online radio goes, you have a few options to choose from. Michael mentioned internet-radio.com and Shoutcast but there are plenty more applications you can use for a project like this. When it was time to play the audio, he decided to stream it using the python-vlc library.
If you found this interesting, we really encourage you to check out the complete project breakdown written by Michael Horne himself. You can also visit his official website for more cool Raspberry Pi projects.