So today I download the source to the Nintendo DS version of the Anguna to see if I could easily get it to build, to push the new level to it as well.
Didn't turn out so well so far.
The development kit for GBA and NDS development (devkitPro) has both the compiler toolchains/build tools/etc for development, as well as some libraries for interacting with the various platforms. The libraries are mostly thin wrappers around the basic functionality (nice names for the various registers, utility functions to deal with them, etc), but there's a few other bigger bits, such as sound libraries, etc.
On the GBA, I didn't use any of the devkitPro libraries directly, and instead just managed my own, using just the simple register definitions.
On the NDS, I ended up using a lot more library calls from devkitPro. Which turned out to be the problem here. The NDS libraries on devkitPro have changes significantly in newer releases. And I'm having trouble coming up with a version of the library from 2008 that works properly. Unless I can magically come up with a working version of libnds circa 2008, the only other solution is to rewrite quite a bit of code to work with the newer version of libnds. No thanks.