I tested out myself. 4TB double sided SSD (Seagate FireCuda 530 without heatsink) perfectly works on Dell latitude 5420. 
Hi, I am using Latitude 5410 with double sided SSD of 4TB capacity. I am planning to buy one more laptop (Latitude 5420) but not sure if I can use double sided SSD on this. Disassembly photo showes me that there is enough space for double sided SSD in the 5420 but not sure if it is OK. Do you have any experience with double sided SSD? I could not find singe sided SSD of 4TB capacity. Due to heavy data management on laptop, need 4TB or more....   Thanks
Latitude 5420 with 4TB SSD