- I'm unfamiliar with how the cursor works on the 9927.
- This is the same double-stepping problem. You cannot read discs in MAME on a drive that isn't an exact geometry match, period.
- The 9927 implementation in MAME doesn't have an HSYNC callback or output. One will need to be added. VSync is fine as-is.
- The VRAM is fine as-is, I think. It looks at a glance like both the CPU and display controller can access it. If the CPU really can write it, then yes, AM_RAM AM_SHARE works.