This is not official.
The perimeter of Takhli RTAFB is basically the same in this Google Map as it was in the late 60s and early 70s. I used the Takhli Master Plan from the late 60s and outlined it with the 2016 Google Map of Takhli.
The outside red line is the base perimeter. The inside red line is the 500 meter drift area as described in Army FM3-3, page 5-5.