Vent for Model A upper floorboard

[Neil Mylar LakewoodCA]

I've been sorting through parts that I might take to the Big-3 swap meet, next month. I found an original upper floorboard with an original accessory AC vent in it.



Well ok, it's probably a heater vent.

There is a rectangular metal box that attaches at the back (see last pictures) and that must have attached to the heater. Would this have attached to a water heater device or a manifold heater? Does anyone have a heater that vents from the floorboard? If so, can you show a picture?

Thanks, Neil