I love the change history comments. They show a high level of attention to detail and craftsmanship, at a time long before source control tools made this kind of thing obvious (and honestly, even after CVS/SVN/Git it still wasn't obvious to a lot of people).
This post also makes me think of the famous 'No Silver Bullet' essay[1], which in 1986 predicted that software would more or less continue to be written they way it was then, by programmers, painstakingly, one instruction after the other. The similarity of the game engine code (along with the comments) in the OP, to something I might have written today, bears this out, I think, almost 40 years (!) later.