It is a working in progress? or you can show something?
Not now. IMHO your project is way advanced in time.
My idea is basically to use the first 64 KB fully as screen RAM. And display it for example as 16*32 (MODE 0). So the screen is four times more high than width.
This way you put GFX only once in the first 64 KB, the background. It stays there as long as you use this particular pin ball machine.
The big advantage is that you actually only have to scroll um and down, but don't need to write background GFX anylonger. All CPU time would be left to animations (Sound, math, etc.)
It doensn't have to be in that format you can make the screen more width too if you like.
But how so often, I kind of miss the time at the moment to realize it that way.
I'm really looking forward to Pinball Dreams from Rhino!!!