Hi hgedorn,
Have you updated to m2? Did you succeed? I have an iMac 2017 27 'and i will make the change in the i7700k processor, hd ssd crucial 2tb. Memory changed to 64 ddr4.
I await your information and comments to buy the 2tb m2; I want to access the system through this component and if it works out with you I will buy the board.