The mirror has a face chip. If you read on, it's Al and SiO2 coated, mil surplus, 2.5 inch hole, and supposedly 1/10 wave or better as originally spec'd out. Near as I can tell it's an f11-110in. focal length. With the right secondary you could cover the chip and fold the light back down the tube to a third element making the tube shorter.
It's in a black anodized aluminum cell held in by 3 clips-very sturdy. I'm asking
$125 OBO and I'll ship.