Retina 5K iMac 27" A1419 Mid 2017 Logic Board W/4GB AMD Radeon Pro 570 - Part Haven
OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com
How to Upgrade iMac Pro Processor (CPU): EveryMac.com
What Does It Take To Upgrade a 2012 iMac 21.5"?
Apple 21.5-inch iMac review | 2014 | Digital Trends