How to Install/Upgrade the PCIe SSD in a 27-inch iMac (Late 2013) on Vimeo
2013 iMac teardowns reveal SSD slots, soldered-in CPU in the 21.5” model | Ars Technica
Amazon.com: PCIe NVMe Gen3x4 SSD 1TB 512GB 256GB 128GB 3D TLC NAND Flash Hard Drive SSD Replacement for Macbook Air 2013-2017, Macbook Pro Retina 2013-2015, iMac 2013-2017, Mac Pro 2013, Mac Mini 2014 (1TB) : Electronics
27" Late 2013 iMac Full NVMe SSD Upgrade - YouTube
DIY 2013 iMac SSD Upgrade! - YouTube
256GB PCIe SSD Install Kit Apple iMac 27 A1419 Late 2013,Mid 2014,2015 Retina 5K | eBay
SSD Upgrades for Apple iMac 27-Inch Late 2013 - 2019