If I understand the problem correctly it has a pretty simple solution that I have done before. Make a new partition on the destination and dd if=/dev/diskAsB of=/dev/diskXsY
where A is the source disk and B is the source partition and X is the destination disk and Y is the destination partition. You may have to run fsck on the destination afterwards and maybe a gpt repair tool.
Honestly though, since it’s an ext filesystem, if it were me I’d just mount the source and dest and rsync.
A few days ago I was messing with my ubiquiti dream router and its ssh config option said the key should start with ssh-rsa 🙄