Help Identifying a Negative Carrier...

Hello all:
Question 1: Can anyone identify what enlarger this 6x9 negative carrier is for?
Question 2: The left piece fits nicely over the right piece. When in place it leaves the cutout shown on the top of the right hand piece. What is this additional opening for?
Thanks in advance.
Todd

I don't recognize them, but don't ignore the possibility that this may be designed for something like a machine printer - not an enlarger.
The cutout could be something as mundane as a modification designed to work with a storage container or rotatable, multi carrier holder.