Sorry, but this is not correct.
The only cMP model with delidded CPUs is the DUAL CPU 4,1.
The single CPU 4,1 or 5,1 and the DUAL CPU 5,1 all use "normal" lidded CPUs.
The Backplane and CPU tray of a 4,1 have SMC number 1.39f5
The Backplane and CPU tray of a 5,1 have SMC number 1.39f11
These SMC numbers have to match , so you cant combine a 4,1 Backplane with a 5,1 CPU tray or a 5,1 Backplane with a 4,1 CPU tray.
If the SMC numbers dont match, the MP enters in failsafe mode and all fans will run at max rpm.
The reason i thought boards are the same, even i dont have a 4,1
It's because both my MacPro5,1 2010 were manufactured in 2011 and 2012,
According to serial number on the back.
In macserialnumber info website.
but chasis board say 2009 on both, printed on the pcb as gold coated copper trace.
Also the fact that 4,1 can be flashed to become 5,1 and both have same chipset: X58 in single CPU tray, 5520 in dual CPU tray.
Same ich10 SATA-II 3Gbps controller on the PCIe board.
Same aluminum case, different than 1,1 2,1 3,1 2008
And also because 5,1 2012 is also the same as 5,1 2010, the only difference is the 2012 SMBios does Not allow to boot OSX SnowLeopard, like 5,1 2010 and 4,1 2009 do,
5,1 2012 can be flashed to become 5,1 2010.
Anyway... I stand true when i say:
i swap trays from 5,1 2010 to another 5,1 2010 and work ok,
dual CPU tray to single CPU tray and back, No problem.
The Bios Firmare is on the chasis board. Not on the tray board.
If one MacPro5,1 case has FW 138.0.0.0
And the other has FW 144.0.0.0
Swapping trays does Not change the FW.
FW 144.0.0.0 is very important, has support for NVMe Boot in OSX HighSierra, and better USB Keyboard support.
Some wireless usb keyboards do Not Alt/Option Boot with older FW, required wired usb keyboard.