Car radio speaker cabinet (Kelsall CW6)

A Toshiba speaker cabinet designed for use with a slot in car radio. It has guide rails and a fixed mono plug at the back so I imagine it was for a very early model car radio. I would have thought that it could be adapted for slightly more modern radios.
Cabinet: 11"H x 8"W x 7"D (approx 280 x 200 x 180mm)
Slot: 2 1/4"H x 7"W x 5"D to stop (approx 60 x 180 x 125mm)