Finally got through that test screen hurdle. A lot of 06xx and 5xxx custom stuff to figure out. In the end I decided it was worth the time to just work though the disassembled Z80 and document everything. I figured out about 80% of it all. It was actually pretty fun.. I haven't had to do so assembly since college. ;)
That allowed me to pinpoint exactly where I was running into trouble.
Then I ran into some Z8002 instructions my core didn't support yet so I put in a simple workaround until I can get that stuff implemented.
I also wrote up an arcade video to LCD interface so I can work on the design without needing that arcade monitor.
Long story short... I'd say we're making some headway: