Is this class of dropship a canon real one that was completely forgotten about? Its not in MUL.
Most likely not, for a number of reasons. Firstly p69 gives no solid stats - its just a re-use of the image from the Inner Spere section with slighly different wording. You'll note it says 'possible contents' and nothing more.
Secondly the Behemoth write-up on p66-67 makes no mention of a Clan version. The Clans don't tend to up weapon cargo DropShips - chances are they are using the Inner Sphere version of the ship.
Now that doesn't mean there isn't a Clan version, its just that we don't have anything to confirm the existance of one.
Hope that helps,
Chris