I installed the PCIe SSD on this EMC2638 machine. All works just fine. Used parts:
M.2 PCI-e NVMe SSD Adapter Card: https://tinyurl.com/y48xoh9z
Kingston A2000 1TB M.2 PCIe 3.0x4 NVMe (SA2000M8/1000G)
Make sure to get torx5 screw to fix the SSD card in its place as the screw doesn’t come by default.
It is very easy to crack the glass in front of the LCD during this step. I used the guitar pick, maybe it was too thick… crack is just on the frame but anyway it is disappointing :(