The fullscreen problem was solved by istudy in this post:
https://www.mobileread.com/forums/showthread.php?t=39802, it amounts to simplifying the logic, and adding a flag, as opposed to relying on the GDK api for determining if you're in a fullscreen state.
I managed to figure the button configuration out eventually, and now I have mostly the same mappings as Adam B's 8.14 release.
The busy LED keeps flashing after going into fullscreen mode, and after coming out. as well as when you press a button that has no defined action in the current view, like pressing the TOC button in a txt file with no table of contents. It stops if you page up or down, so I'm not too worried about it.
Currently I'm having fun trying to work out how to port the refresh mechanism, it sort of works, but that might have to go on hold, as my wife has just gone in to labour!