HP 10529A Logic Comparator - interesting option pod

[pamphonica]

Here's one for what our beloved Dave calls the "fanboys".
I bought a nice HP10529A logic comparator and it came with an accessory I've never seen before.
Simple reverse engineering shows it to be a pod that allows 5V to be fed into the comparator, and it just turns it into a large logic clip!  All 16 inputs from the physical clip are pulled up with 10K resistors, and that's it.  The LEDs on the comparator just show the logic state, I assume. 
The part number hidden under the plastic moulding is 10529-60013.  It doesn't seem to appear in any of the catalogues I have.
-Jeremy