Jens, maybe I can help. Here is an X-ray of the area on the A4000T mobo, with some overlays:
Lisa is blue, you have to avoid the red areas:
1 = Forward stand-off point for the accelerator
2 = PAL/NTSC jumper block
3 = Capacitor
4 = Keyboard connector
5 = Discs Module (SCSI etc)
The green is where I reckon you can build, if you keep the Indivision lower than the accelerator board.