This is the iPod I use daily, My 2004 iPod 4G, and I absolutely love it! I use it with Rockbox because iTunes is genuinely awful, and I much prefer being able to drag and drop MP3s directly onto it. Inside, it has a 64GB SD card installed via an iFlash adapter, which works perfectly with this iPod model.

Here are some more photos of the inside for those that are curious.