We're getting off topic here, but whatever.
I don't believe there ever WAS a dedicated ESB board set. I believe Atari supplied Ops with a kit to convert their SW boards back in the day.
So if you have an ESB board, you basically have a SW board with a kit on it - either Clay's, Spaeth's, Vectorlabs, or the original OEM kit.
I could be wrong. In fact I probably am. I tend to talk out of my ass a lot and make shit up. But I thought I read somewhere that ESB was a kit sold by Atari for Ops to convert their boards.