@RDan
At your place i would have plug the hard drive in another computer already and installed from there then re plug the hard drive in the laptop.
Afterwards to update LibreELEC it will easy just copy the .TAR file in the .update folder or use the built-in update feature, you won't need to do all that.
Your laptop obviously has a problem with booting a GUID partition table and even the last trick i showed you with Rufus might not work for you.
EDIT: I think for the "sda1" to work you would need to format your hard drive in two ext4 partitions with a linux live cd first but i might be wrong here.