Installing the games (on Windows 7)
● Set Windows language to Japanese.

● Install the game from CD.

● Set Windows language back to English.*

● Download the SDK zip file (https://tenka.seiha.org/2019/01/overdone-angel-spaghetti-code/ -- under "Galaxy Angel Tools and Files"). Extract it to a folder. One of the folders should have a file called "gapak.exe".

● I would then open the Command Prompt (by opening the Windows Start menu, choosing "Run", then typing "cmd" and pressing Enter).

● I would then drag "gapak.exe" into the Command Prompt window.

● Then in the Galaxy Angel install directory, enter the "Dat/" folder and find the ".pak" file I wanted to extract. Drag it into the Command Prompt window.

● And then drag in the folder I wanted the files extracted to. Press Enter.

* Using the Command Prompt in Japanese would give me errors. I assume because it interpreted the backslash ("\") as a yen ("￥")? Changing all "yen" symbols to a "backslash" might fix it? If it is successful, the Command Prompt window will quickly list the filenames as it exports them.

This would extract the contents of the ".pak" archive into files I could identify. Images like ".BMP" and ".PNG", or audio like ".IIDX". There were other files I did not recognise. 
The ".PAK" file ending in "020" seems to contain assets for the 3D space battles, like textures and explosions. It is possible the ".X" files contains the 3D models, but that is very complicated to decipher. I do not know how to extract 3D models.
The contents of the 041 and 042 ".PAK" files appear to be identical to 031 and 032. In "Galaxy Angel" they are in lesser quality. In "Eternal Lovers" they have a vignette.