It isn't soldered in, but it is screwed to a frame which in turn is screwed down. Take out the screws, and remove the connector. The release tab breaks off easily (as you've found), so connector removal takes a little work. Gentle prying with a utility knife will separate the pieces enough for you to get a small screwdriver in there. After that, it's duck soup pulling off the connector the rest of the way. Just work slowly and carefully.
A 40GB drive might be overkill (personally, I'd save it for a more powerful 'book). One issue that you will encounter is the need to partition it into smaller volumes, each less than 2GB in size to avoid problems (the actual limit could be larger than that, but obeying the 2GB rule will definitely work). Given that little annoyance, you might want to choose a somewhat smaller drive (which will still be huge for anything 68k-related).