103: I'm not sure where you are on your knowledge of Colt Conversions before Colt came out with the Open Top, which wasn't a conversion, but a new model. Don't take offense, but everyone had to learn sometime. If you are already well informed, someone who reads this may find it new. First off if possible read Bruce McDowells book on Colts open top style revolvers, their heritage and history. It's not a easy to find book, someone you know may have a copy you could borrow. Also Dennis Adler wrote two excellent books on Colts. 1) Colt Single Action and 2) Metallic Cartridge Conversions, both give history, production, and a lot of info on the various Colt conversions, both can be found online. Several older books by Charles Haven and James Serven are chuck-full of Colt model history and info. 12-15 years ago until I read up on them, I knew squat about them other than they existed. I'm by no means an expert, others may jump in and either correct me and/or add additional info.
You basically had three Colt conversions using the Army percussion revolver.
(1-The Richards, (Colt engineer Charles Richards) had the rear sight on the conversion ring, a rebounding firing pin within the frame, and a ground off hammer with a flat appearance, and a ejector system that used the existing lug holes for attachment.
2) The Richards II, which was a refinement of the original (or Richards I as some call it) in that the rebounding firing pin in the frame was eliminated and the hammer was outfitted with a pinned firing pin. The conversion ring was refined. The rear sight was taken off of the conversion ring and a notched hammer as in the original 1860 Army was reintroduced as the rear sight, also the original ejector system was retained. Another Colt engineer, Richard Mason helped with this change
3) The Richards/Mason. These conversions used all of the changes of the Richards II, but Mason designed a new cartridge ejector that eliminated the use of the old rammer lug hole and the ejector was screwed to the barrel. A lot of 1851 and 1861 Navy frames were also used in the Richard/Mason revolver model. In the first two conversion models, Colt used existing 1860 percussion revolvers and parts to produce them. The Richards/Mason did also, but a lot of the parts were newly made. After these three models, Colt then came out with a newly produced model, not converted from percussion revolvers, 'The Open Top', which resembled the Richards/Mason in a lot of ways, but was produced from all new forged frame, cylinders, and parts. The Open Top had a non-stepped frame and non-rebated cylinder, it had a pinned firing pin on the hammer, and the rear sight was forged onto the rear of the barrel. I've left a lot of 'holes' here and there in the run of these revolvers, but gave the basics of them.
In answer to your questions, all of the Martial Richards (Richards I), would have had the face of the original hammer ground off flat to resemble in a lot of ways what can be found on original Ruger single actions before the transfer bar models. There was the rebounding type firing pin in the frame to strike the primer.
The answer to your question about anyone selling a conversion ring with the original Richards rear sight on it, haven't heard of any. Fox Creek Kid who used to post a lot on this forum had someone make him a Richards I style revolver onetime, but it cost some dollars to do to convert. You change over to that, then you'd need to convert the hammer to a flat face to strike the rebounding firing spring. The Richards I conversion ring was a bit bulkier also vs the Richards II if I recall right. Hoof Hearted who posts once in a while is a working gunsmith who has done a lot of conversion work, even fabricating his own Colt Thuer copies. I'm not sure if you could remove the conversion ring on a Richards II that you advise you're going to buy and replace it with a Richards I unless a lot of fabrication was done. 45 Dragoon who posts on this forum does a lot of tuning and special applications to open Colt style revolvers, but I've never read where he does the type of 'conversion' of a Richards II back to a Richards I. Coffinmaker who posts on CAS says he's a retired gunsmith, but he seems to be doing a lot of things all of the time, but says he's not looking for business. There's some 'plugs' for you guys.
From all of the books I've read on why Colt went to the Richards II from the 'I', it was for dollars. The Richards I was expensive even during those times to convert, so that's why they dropped the original Richards which saved them dollars. From what I've read, Uberti probably will never offer a copy of the 'I' due to the fact they can make the 'II' so much cheaper and feel that there wouldn't be enough demand to cover costs. I'm just happy they produce the Richards II, which is my favorite of the four I have, a RM and two Open Tops, plus the Richards II. If it were me, for the cost of converting a already conversion replica back to it's parent model, I'd leave it as is due to the cost involved. During your presentations to visitors at living history events I'd just lay out the Richards II you intend to buy and explain how Colt converted the percussion guns to cartridge if that's what you want to do and tell them ya got Junior instead of PaPa and possibly mention the RM and Open Top. Ya could advise how the Open Top was the forerunner of the famous Colt Model of 1873 that probably most have seen in a multitude of westerns. I bet the majority of them have no idea and a lot of them wouldn't give 2 cents what one you have for display. Well if you and all who read this are still awake after reading all of this (I never get windy), hope it helps and informs. Like I advised earlier, I left a lot of smaller detail out and 'an expert' may need to correct me. "Good night Mrs. Calabash, wherever you are"! Crow Choker
Note: Added Jan 09---Yer right Abilene--The Richards II retained the notch in the hammer for the rear sight as in the original 1860 Army (as did the Richards/Mason models). Musta been thinking Open Top which had the rear sight on the rear of the barrel as you penned. Don't know why I penned it that way, I've sighted down that Richards II enough times since getting it back in 2008 and also my Richards/Mason. I corrected it above in the post. Thanks for the correction, Yer a Gentleman and a Scholar.

CC (If yer reading this thread for the first time, this note was added after Abilene posted below this posting)