The split washer goes here between the arbor nose and the Arbor's bottom seat.
It does just rest in there to fill in the slack.
Each time you dissemble the gun to clean, you will have to remember to drop it in again.

Nice.  Grips look like Uberti's SAA competition grips via various importers.  Coffinmaker should be along to tell you that it won't be worth a damn until you fix the short arbor  .  See if you can drop a #10 split washer (or whatever) down the arbor hole and still get it to go together.  Do you know how old it is?  Some of my newer ones didn't need this.  But it tightened up some loose arbors on my older well-used conversions.

Looks good.   

I recently bought this open-top in 45 Colt. After getting it I realized the grip frame (backstrap and trigger guard) were not original to the revolver nor were the grips but I decided I didn't care. I striped the blueing from the revolver because I wanted it to look older and used but not abused. The guy who owned it previously had buggered the grip frame screws pretty bad so I ordered new ones and replaced the buggered up ones. I also cleaned and honed the rough edges from the internal parts and lightened the hammer and trigger/bolt springs and it is much smoother now. I haven't yet made it to the gun range to see how she shoots but hope to before to long since I have a new rifle I want to shoot as well. Here is what she looks like.

My Uberti has a good barrel and I wanted to try it out at longer ranges so its got a soule style tang sight (I made it) with adjustable eyepiece and a Lyman tunnel foresight with changeable inserts