For a long time, the traditional line was that doing anything parser-y from scratch was a fool’s errand. Many people would come in, enthusiastically announce their intention to work on a custom parser, and then disappear when things got rough.
Recently, though, more people have been sticking. Linus Åkesson has created the Dialog system compiling to Z-machine, which you may be interested in looking into:
Robin Johnson has made a custom parser named Versificator and a follow-up Versificator 2.0 with clickable GUI. He’s won IFComp with this setup.
Finally, there’s a group on here that have figured out how to recreate ZIL, infocom’s original parser. Searching for ZIL should bring up numerous posts.
Of course Parchment, Quixe and Vorple are also the state-of-the-art, but you seem to be well aware of those and their creators.
All of those took quite a lot of work to get done, but they should give you some idea of what’s necessary. Good luck with your work!