If you look on page 291 of my Gas Pump Identification book, you will see that not all 300 had a sight glass. The pictures I used when writing the book came from an original Tokheim pieces of Sales Literature. These pictures do not show a sight glass on the pumps.
As you mentioned, and I sort of remember (I have owned a number of 300s) a sight glass being near the top of the nozzle side of the pump, as shown in the picture of the 300 Twin.
You might also notice that there are five different 300s shown in my book, who knows, there might be more.
If you don't have a copy of my book, just go to my website:
www.petrocollect.comJack Sim