RE: unknown cox
That engine is a Keil-Kraft "Cobra" .049 made in Hornchurch, Essex, England sometime in the 1960's.
I don't know how many they made but it was not up to Cox standards for performance so it is probably fairly rare and valuable today.
A lot of engines that don't measure-up have a tendancy to fall by the wayside...which means there are fewer around.
Clean it up and show it off.