Alright, so I become stuck on box2d4d not only with the custom memory management code, but also with all the pointers, of which Erin Catto is a fan of. I didn't really have time to deal with the pointer problems, so I'm taking a different strategy.
There is already a java port of box2d, so I'm taking that code and porting it to D. I already got it to compile. After I get some examples working, I will then add doc comments, upgrade it to the latest box2d version, and perhaps the re-implement custom memory management.
The box2d4d project already has more files than my own ArcLib project has, to give an idea of the scope of the project.