That box looks like a straight-forward unaltered VS410.
It's been hacked up at least a little - for example, there's a toggle
switch mounted above the external RD5x connector that doesn't belong there.
And there's another D connector labeled "Trimarchi bus" that doesn't
belong.
The little 1" high extension on the bottom is standard DEC issue, but
originally it just held the extra connector for the expansion RD5x box. It
was mostly empty space. It's certainly physically possible that somebody
could have stuck a single board -11 (e.g. a KXT11 or something) in there.
It'd fit; there's plenty of power available, and you could wire its console
to one of the uVAX2000 serial ports.
Whether that's actually what's been done in this case, or better yet,
exactly why somebody would create such an abomination, is unknown.
Bob