Why wouldn't they be able to pretty much just reuse all of the old engine code, if this is just a graphical update? Changing the graphics without changing the rest of the game should be fairly straightforward as long as it was written reasonably.
void DragoonAI()
{
// Decide next move by reading main video buffer for random bits
MoveDirection = Video->buf[1000];
...
}http://www.codeofhonor.com/blog/tough-times-on-the-road-to-s...