Iver Johnson 3rd model 32
Bill, I popped the grips and the serial number is A 87706 making this a 1913 production.
I compared it to the photos and drawings in your book as well as two other 32 Iver Johnson top breaks I have, and they all have some sort of protrusion in front of the cylinder which holds it in place.
This cylinder is flat on the front, pops up when the extractor pops up, and can be pulled out with finger pressure.
It appears I am missing a small piece, but I don't know what.
Any help would be appreciated.