This is for Torment of Velious version:
For me, it was further north than the location pictured above.
I was able to get him to spawn at location -3983, -18, -297, specifically in front of the dragon throne east side. Was spawned next to a second giant, from what it looked like these periodically roam back and forth in front of the dragon throne. He also spawned at the west side of the dragon throne at loc -4004, 466, 295, at this particular spawn he did not roam back and forth.
Respawn time of named/placeholders is 8-9 minutes.