
Well Hey There Lou

Heard my name called (I think), so here I are.
First and foremost, Lou, that sample example you show is of the "ope top design" but isn't exactly the model know as "The Open Top." You gun is a Uberti built Richards/Mason Conversion with the later "S" lug barrel assembly. It probably has the same "Arbor to Barrel" fit issues as most all other Uberti "open top" replicas. Maybe not, but the odds are it needs corrected.
The "ARBOR" is that great big round rod sticks thru the cylinder in into the Barel Lug. Wedge gores thru the end in the barrel lug, holds it all together.
Yes, a #10 split washer is a "one coil spring" except if it the correct thickness for the fix, pushing the everything together compresses it completely and the wedge snugs everything up nicely. An inexpensive fix that's quick. The Wedge may well net to be re-fit after the fix.
Your gun also, as pointed out, has Navy/Model P pattern grips which for many is a plus. I personally prefer the longer 1860 Army pattern grip sets.
If not already done, you may wish to change-out some springs. I should personally suggest the Lee's gunsmithing Gunfighter Spring kits. It's a nice light Main Spring that doesn't stack. Includes nice wire Trigger/Bolt Spring. My other recommended trigger/bolt spring is an OEM Pietta SA trigger/bolt spring. Changing the Hand to coil spring and plunger is a mite involved on an Open Top and you might well need some professional assistance there.
The Open Top Guns, especially the Conversions are UBER FUN!!! Enjoy yours.