I think the best way to do this conversion is type in the BASIC listing as comments, and then add our Z80 conversion of each line as we go. This will all be stored in our main.z80 file. That way it will be obvious what code each line translates to, and hopefully be easier to follow.
Note that this isn’t going to be the most optimal or efficient solution to converting the game, as optimising everything often leaves the code being somewhat unreadable. I’ll offer some thoughts on how it can be improved, but I’ll leave that up to the reader 🙂