Look carefully and you will see that Colonel Crittendon's mustache is upside down for the entire episode.
Hogan says they have to kill the scientist because he must be working on an atomic bomb. In a later show Hogan is given the name of the "Manhattan Project" by a German but Hogan does not know it has to do with an atomic bomb. Both of these can be true as atomic energy had been known for decades, but the actual use of an atomic bomb was secret until dropped.
The idea of using a crossbow as an assassination weapon is not far fetched. A specially made crossbow was available in the OSS equipment catalog.
The license plate on Klink's staff car is WH 65047.