Glad to see some interest in Ozmoo, which I co-wrote.
Ozmoo is open source and may be ported freely. We will be happy to answer any questions that may arise too. I admit Ozmoo and its build system are a bit complex.
When considering tools to write your own Z-code games to be run on an 8-bit computer, performance is an issue. Any non-trivial game created in Inform 7 will be painfully slow on a typical 8-bit machine. A real-world game, if it can even run on an 8-bit machine, may take several minutes to process each command. This is due to the way Inform 7 was designed and developed, where performance on machines slower than say 1 GHz wasn't really considered.
Inform 6 is fast enough, as a language. However, it comes with a quite powerful standard library, which has become more and more complex over the years. A game compiled with library 6/2 may be quite fast, but a game compiled with library 6/12 will most likely feel sluggish. However, so many bugs have been fixed in later versions, that it would be painful to use the oldest versions. Also, z3 games require a smaller interpreter and may therefore be a better fit for 8-bit machines than z5, but the Inform 6 library can't be used to build z3 games.
ZIL is probably the best option right now. It's fast and powerful. As for the syntax, it may take some time to get used to. There's an active and friendly group on Facebook called ZIL - Zork Implementation Language, where you can get all the help you need to get started. Also, the ZIL source code for all Infocom games was published a while ago, so there's lots of code to learn from.
We are currently working on a replacement library for Inform 6, which has performance on 8-bit machines as its main design goal. We're aiming for a parser which feels on par with Zork I, while keeping the code small and fast. Also, we're planning to allow authors to build z3 games using this library.