Hi Hansel,
I was hoping you might chime in on this (pun intended!), as I know you've spent a lot of time with No. 4.
To my eye at least, it looks like the bell on Monson No. 1 in the old photo does indeed have the rib or groove around the lip that No. 4's bell has now, but I don't have access to any higher resolution images to verify my interpretation. Also, wouldn't it be natural for a bell to be shiny when it was new and then get steadily less shiny over the next 100 years?
I agree that B&SR Nos. 7 and 8 carry their original Baldwin bells. However the bells on the Monson engines, both now and back in the 1930s when they were photographed by Linwood Moody, are not their original Vulcan bells.
-Philip Marshall