I'm not sure what your question is. I would do something like this: shutdown VM, backup (without the passed through disks), copy backup to new node, restore VM from backup (on new node), shutdown both nodes, transplant the physical disks to the other node, start nodes, double check and fix paths to passed through disks, start VM (on new node) and delete VM on old node. Plan each step carefully yourself!
Like this post can we move VM from old node to new node.
Thank you, kindly! I was able to transfer the config files to the new node and was impressed to see the VMs populate almost immediately. Taking your tip to remove the config files from the former node to prevent any collisions if both instances were to boot at the same time, here are the steps I took, in case a step-by-step guide helps anybody else. I'll refer to the old and new nodes as Node A and Node B, respectively.
Shutdown the VM and confirm its status is "Stopped" in the Proxmox web GUI
Log into Node A CLI, browse to the config file directory and rename the config file. The VM will disappear from the web GUI. cd /etc/pve/qemu-server/
mv 123.conf 123.conf.bak
Create a directory to store the config files on a shared mount point, accessible by Node B (useful as I was migrating several VMs at once) mkdir /mnt/pve/[shared]/pve-conf-files
Copy the config file from Node A to the config folder on the shared drive cp 123.conf.bak /mnt/pve/[shared]/pve-conf-files
Log into Node B CLI, browse to the local config file directory, and copy the config files over from the shared drive cd /etc/pve/qemu-servers
cp /mnt/pve/[shared]/pve-conf-files/123.conf.bak .
Rename the copied config file back to its original name mv 123.conf.bak 123.conf
The VM will now appear in the web GUI for Node B and may be started normally once it has loaded.
This wasn't that difficult, in the end, though I'm surprised that all I needed to do was move a configuration file that was only about 10-20 lines of text in many cases. This method didn't copy over backup settings but those are easy to replicate if I make sure I've documented things before taking a VM offline.