I will make new pictures, with more detail of the chips you mention.

If I connect the board to the 512, I get a bong and a black screen. No effort is made by the Mac to start from a floppy. Since I have not found the time to try to make a good startup floppy, I have not seen the Mac boot completely. However, without the alien board, the Mac gives the blinking disc icon and you can hear it scan the (faulty) floppy.

Jelle