I have found this same visible pump twice, only mine had the Martin & Scwartz top instead of the Rush conversion piece like that one. Both of them I believe were model #100 (I'll check next week when I'm over there). Bill Bahorik in PA owns them now, and they are restored very nicely. I was hoping that when I found the second one, it would be marked Salisbury, Maryland on that access door but they both say St. Louis like yours. Of course we know they (M&S) had two different plants which manufactured pumps. Those gallon markers are correct and identical to what were in mine. Good luck, you can do it!
Goober
