[Arran]

  I believe that removing the head unit from the dash would probably answer a few questions, like who made the unit and whether someone drilled and cut holes in the dash to fit it in there. The other radio linked to on fleabay isn't an I.H factory radio either, it's a generic aftermarket under dash unit, such units were marketed by many radio manufacturers to fit into older cars or trucks, some were self contained and others were two piece with the tuner in one box and the amplifier, speaker, and power supply in another box.
Regards
Arran