The Corona has 2 similar chips labelled as "NEC 8817 KX (C) SCISYS". As a lot of 74... logic ICs found in other 65C02 chess systems are missing, I guess this is a custom chip manufactured by NEC for SCISYS which incorporates all of the missing logic chips. The Corona comes with a W65C02-8 (MHz) CPU and a 5 or 6 MHz quartz. It can easily be tuned to 8 MHz just by changing the quartz.

So I doubt that the custom chip is the reason for your tuning problems. Note that the pinout of the W65C02 is not fully compatible with the R65C02, so you cannot simply put the W65C02 into an R65C02 socket.

Furthermore, the W65C02-10 (MHz) ist doubtful. I bought 10 of these in China. It turned out they had the same pinout as the R65C02 and were no faster than 5 MHz. Some did not work at all.