Steel machinist clamp and block

Description

Steel machinist clamp and block.
To be honest, I have no clue what this steel block is. I'm familiar with CnC blocks, Milling blocks, machinist blocks and clamping fixtures but I'm unable to properly pinpoint what this exactly. It has tool cut pathway marks and it's made from a tool steel (not mild or high carbon steel).
It measures 11 7/8 inches long
Wide it measures 3 7/8 inches
Thickness is 1 3/8 inches with a
slot cut into the middle of the block for tool or drill bit path (or so I assume).
Both angles on the block are 2 inch angle with a 3/8 inch contact pad on both sides.
It weighs 17.5lbs
I've checked the straightness with an old school "Great Neck" adjustable Square ruler and it is dead straight on all sides I checked.
(MAYBE a thousandths to 2 thousandths gap where the angle meets the block deck)
Screws securing the angle iron clamp are machine threaded (very fine thread)
There are numbers stamped into block under the angle clamp, numbers are (4, 4, 4,1) on the left and (4, 1) on the right.
if anyone knows what exactly this is, please feel free to let me know.