With help from Easycor, I got the old "mapmaker" utility working, and I used it to create an accurate terrain of the central Philippine islands. I will be using this as the basis for some offline missions. At this point, it works great with Aces High 1.11.4 and Aces High 2.12.4. The current version (2.28.x) should also be able to use it as a "converted terrain", but I have not yet tried that. Here's what the map looks like:
I will be publishing this terrain soon. Stay tuned!