Gotcha. I just double-checked to make sure I didn't write it down wrong, and the chips in Mattel Chess are unfortunately 0601s.

SCU=MOSTEK>SGS-THOMSON>STMICROELECTRONICS is very interesting. I've decapped a few Mostek chips- I'll go back and look at them and see if I notice any similarities to the SCUS chips. It seems like they all have Mostek on the die somewhere, though.