Quoted from nitrocow:May have one backwards.
Look at the same board at Pinwiki. The ROMS on that board have the notches at the bottom. It appears every other chip on your board in the photo you posted also has the notch at the bottom.
https://www.pinwiki.com/wiki/images/1/1e/Sega_WS_CPU_Sound_520-5136-16_Rev._D.JPG