FWIW, it looks like the Radio Shack 40-1228 started out as the foam covered Heppner version sometime in the 60's and was replaced by the Japan/Foster made version circa 1975, and i think this is probably the time the snap on plastic covers entered the scene. In the '68 and earlier catalogs they made a point to mention they're made in USA, the catalogs continued to use the same stock photo thru '74. The years i was intimately familiar with RS(75-81) you could depend on the accuracy of the catalog images, they were of course masters of advertising.

The 70's RS/Foster versions are really very good sounding units for their entry fee, as OG says, they're fairly delicate and won't tolerate abuse. At some point in the early 80's they changed the horn to all plastic, and i think the country of origin became Korea(not so good anymore).