This object is a "MOS CONTROL" module from a KL10. It is an extra deep 6 high DEC format multilayer (probably 4) PCB. It has front and rear stiffeners.
Manufacturer
Digital Equipment Corporation (DEC)
Identifying Numbers
Model number
M8576
Printed on barcode sticker on bottom of board stiffener
Model number
M8576
Etched near left edge of circuit side of board
Model number
M8576
Stamped in red on front of board stiffener
Other number
5012900D
Etched near left edge of circuit side of board
Other number
MR2131A444 B
Printed on barcode stickers on bottom of board stiffener