mystery hole in rear bumper deck

[Lindsay McConnell]

Could it have been where an extension/accessory spare tire inflator was mounted?

[lamacchina]

This car is very original.  I don't think it ever had air shocks.

[bcudajoe]

If the car had rear air shocks installed at one time, this hole could possibly have been used to mount the fill valve?

[lamacchina]

I recently bought a '50 special deluxe convertible.  It has a square hole in the rear bumper deck.  Any ideas about what might have been mounted there?