I have a piece of sales lit. for the G 500 if that is what your pump is, will try to post it tomorrow, it's in color.
A little info. about dating visible pumps.
First visible was the Fry, (I think it was a Fleckenstein but I can't find proof of that) around 1917. Most companies were reluctant to jump into making them so they made visible attachments. Around 1922 the majors started making visibles and they started to faze them out around 1928. The last visible was made by Wayne in 1947. So, if you don't know the exact date it is safe to say "around 1925."
Jack Sim
Author, 1st & 2nd editions of Gas Pump ID book, 3rd edition is now available at
www.gaspumpbible.comAir Meter ID book also available