Here is one showing a C-3 attached to a Bowser 101. thanks charley
Where is the one you say is here? Do you have a photo of it? Did you post that photo?
I will post a photo of the bottom later. The bottom is about 11" in diameter with a 10" diameter plate with a bunch of bolts holding that plate to the jar bottom casting. That piece actually looks to have been added by someone and not really original to the base.
So am I understanding that this upper jar would have been a replacement and not an original pump top to some brand named unit? If so that leaves me to think that it could have fit any pump as needed?