I installed Clear Linux on my old macpro and it is running nicely. Recent releases would not boot but 37840 (gpt) booted into GUI installer and then updated the system to latest with swupd. CL is running on a archaic spinning HD and hoping to install it in a SSD.
The macpro has opencore legacy patcher installed in the macos drive.
ECC memory for this mac is cheap now on ebay. So, it has the maximum RAM to get triple channel working with the two processors.
My next step is to get the CPU only Llama running on it.
FYI, grab the Llama while you can!!