The board you have should be a Centris, maybe someone decided to put a FPU into it and this was the only CPU in reach?

Have you tested the board to see if it runs on 20 MHz?

BTW, i also have a C610, including the rare and in germany nearly unobtainable NuBus adapter. 8-o

I don't like the C610 that much. Problem is, people think the knob on the front is to eject the floppy. :lol: