"...The only thing it doesn't do is bell the case mouths..."
IIRC the decapping rod has a slightly oversized double taper on the opposite end from the decap-pin end.
I can't remember if you use that in a separate operation by turning it around,,or if the length of the rod is supposed to be just right to decap and also slightly flare the case mouth all in one step using the tool to decap & flare.
The decapping rods are very often missing on these Winchester tools. The 'flared'section on the one end is often called the 'peanut' by reloaders/collectors for some reason(?).
There are a couple of guys around especially on SASS forums that make these decap rods w/pin up in the common Cowboy calibers like 44-40, ect.
The small dia decapping pin itself was usually attached w/a small set screw to the larger near case mouth dia rod.
Home made replacements are common but they do the decapping job,,they often just don't have the case flare taper on them though.