I have installed my Indivision AGA and it seems to working with no problem for the normal resolutions. I've installed the HighGFX driver and tried the 1024x768 mode and almost immediately I get screen corruption/flickering, etc. reverting back to a lower screen resolution makes the problem go away again.
I haven't added a heatsink to the Alice chip yet, but I'm fairly sure the A1200 wasn't powered on for long before I tried this so it didn't have chance to get too hot. I was wondering what the other fixes might be? My A1200 is a rev 1B board if that helps.