My second "big" design:
Short video: https://www.youtube.com/watch?v=bxhbQZboVN0

AtariST microATX 1.pdf
AtariST microATX 2.pdf
AtariST microATX 3.pdf
AtariST microATX board.pdf

There was a svereal mistakes on this board. The biggest fault was to connect D0-D7 lines to both 6850 ICs and Yamaha chip. Correct connection is D8-D15. This is adapter to fix that:
fix1.sch
fix1.brd

Also pull-up resistors werent connected to BR, BG, BGACK, DTACK and RESET signals.
Glue should have D8-D9 sinals connected to pins 48-49 instead od D0-D1.
Pin 2 of IC16 should be connected to RW signal.
Yamaha doesn't have GND connection.
22uF capacitors instead od 22pF in Reset (NE556) circuit.