The R&D is sold and distributed by Taylors, and no longer has its own website.
The Kirst website has information and descriptions and a list of dealers (websites) to go to, no direct sales.
The Steel framed Remington is the one you want, and both R&D and Kirst warn not to use the converter in a brass framed gun.
The R&D is a simple cylinder swap, a drop-in, no modifications to the revolver are required. The cylinder is removed to load and unload.
Kirst has two versions, soon three. One is a drop-in, like R&D except for the single firing pin, non-rotating backplate. No gun modifuications. Also requiring removal for loading and unloading.
Both the above work like the Remington in Eastwood's "Pale Rider" movie.
The second Kirst is ported, and requires the user to cut a loading port into the breech of the gun, with a rat-tail file and Dremel tool. This loads with the cylinder in place. (This causes the gun to be "modified" in the eyes of the ATF, for the owner's personal use and cannot be subsequently sold as a cap & ball as it is now a "modern" firearm.)
The third may or may not be available yet, has a loading gate built in to the breech-plate. (also costs more) Kirst also sells an ejector rod kit for the ported versions.
http://www.taylorsfirearms.com/index.html http://www.kirstkonverter.com/safety.html