Finally received the 4tb SSD drives.  Working with ProSupport today, we installed the following drives into the specified physical slots:   Once installed, booting into BIOS, Windows already recognized the drives and booted correctly without any BIOS changes.  Once booted, the drives are named: C: 1tb Operating System (BIOS SLOT-2)  4tb data drive (BIOS SLOT-0) E: 4tb data drive (BIOS SLOT-3) Finally, formatted the new drive. Don't know why the Dell 7760 Specifications guide and Engineering guide are so confusing about configurations and installation of these drives, or why BIOS and Windows number them differently.  But luckily all works fine, and I can now use the SSD access door (with system powered off) and cold swap the data drive as desired.      
Just received my 7760 with 1tb SSD in the primary slot. Bottom panel has the open access to SSD. I have a 4tb SSD that I’d like to use as a hot swap in the primary slot — for data. Can I configure one of the secondary SSD slots for operating system so I can use the access door to swap out data?? 
Use secondary SSD slot for operating system?