Ah, I misremembered. Wikipedia's Macintosh II page says:
"The machine shipped with a socket for an MMU, but the 'Apple HMMU Chip' (VLSI VI475 chip) was installed that did not implement virtual memory (instead, it translated 24-bit addresses to 32-bit addresses for the Mac OS, which would not be 32-bit clean until System 7)."
"The machine shipped with a socket for an MMU, but the 'Apple HMMU Chip' (VLSI VI475 chip) was installed that did not implement virtual memory (instead, it translated 24-bit addresses to 32-bit addresses for the Mac OS, which would not be 32-bit clean until System 7)."