Don Marshall (Boma) was working fairly regularly in guest shots in those days, and had also guested on Roddenberry's
The Lieutenant. A few years later he got a steady job as Dan Erickson in
Land of the Giants.
TOS had several guests I immediately recognized during its first run, including Paul Carr (Kelso), and Paul Comi (Stiles). Glenn Corbett (Zefram Cochran) had previously been a regular on
Route 66.