Hi,
In this case, I'd dd the whole HDD to the SSD if they are of the same size (or if the SSD is bigger).
Else I'd partition the new drive, and copy contents from the HDD onto the SSD. Dont know if it works for /dev and all that....
If that wouldnt work, maybe install proxmox on the ssd on another machine and then use the "proxmox backup procedure" that you can find in the forum.