Installed OK on the MBR-partitioned drive in this 2010 MacBook Pro A1286 once I
* deleted the ext4 partition sda1 which had the entire drive
* created a 1MB partition at the front as sda1 for MBR use. Then,
* created an ext4 partition sda2 for the rest of the drive for root.
Now, Mint 19.1 install is complete, and I can work on the NVIDIA driver issue, serely confident that no other Apple strangeness will complicate this install. {/sarcasm}