How to repair a drive after accidentally changing the partition scheme?
The output from the gpt command indicates the following.


While there is no indication that there is a problem with the primary
GUID Partition Table (GPT) header, the entries appear to have been
corrupted.
The secondary (backup) GPT header and entries are intact.
The MBR tables contains at least two partition entries. One entry is
a OS X partition (type 175=0xAF). Another entry is an OS X recovery
partition (type 171=0xAB).


Under normal circumstances, the following is true. 


The gpt command does not display MBR partition entry for partitions
of type 0xEE.
Some of the primary and secondary GPT headers values differ,
therefore the headers not identical.
The primary and secondary GPT entries themselves are actually
identical.


Therefore, copying the entries, from the secondary GPT to the primary GPT, should fix the partition table errors. The commands give below will do this. (I assume the external drive is still disk1).

diskutil unmountDisk /dev/disk1
sudo dd if=/dev/disk1 of=/dev/disk1 count=32 conv=notrunc seek=2 skip=1953525135 



  Even if the above commands fix the partition table errors, there is no guarantee the data, stored in the partitions, has not been corrupted.