There is a lot less work and documentation that has been done on the GBA versions. However, some people have contributed to make this wiki section a decent source of information. In no particular order:

Drakkhen Early work on the (U) version ROM map.

Everything Work on the (U) version ROM map and specific data format.

Novalia Spirit Provided info with the help of his GBA patches.

madsiur Work on the (U) and (E) ROM maps, some disassembly work.

LeetSketcher Provided info with the help of his GBA patches.