I got it working.
I was suspicious when I did a
ls /sys/firmwareand did not find an
efidirectory. It turns out I had to change around some settings in my BIOS, per steps 1-3 on this page: http://trackballer.com/2014/01/13/enabling-uefi-secure-boot-with-a-gigabyte-bios/ (IOW, stop before enabling secure boot).
I’ve no idea why setting the BIOS to expect Windows 8 and to disable CSM support (w/e that is) gets
grub-installto work, but there you go.
Thanks for the help.