For those who are interested, here is a command line utility to extract and convert GBA Doom 2 maps to PC format from a ROM file.
gbad2_conv.7z
The converted maps will require BSPing.
I have provided a MAPINFO to match up the maps appropriately.   GBA differences to note can be found on the wiki:
Doom II for Game Boy Advance   Edit: I should note if anyone is going to play through these maps, that I have no idea which maps work or don't. I do know the Grosse is not completable without re-tagging the exit door sector. The maps are direct conversions and come with any problems that the maps originally had. e.g. ghost secret sectors.