By the serial number, it's an M0001E. I also checked the code for the Mac Plus ROMs and they are the same. The disk drive is 800k. I don't know enough about these to question the yellow writing. Maybe it's a refurb board? Odd that it's got that blue "512K" sticker on the board and on the metal bracket next to the connectors that you can't see in the picture. Did these boards have Rev levels?