The Kirst 44 Rem Konverter is more historical in the fact that the first Remingtons were converted to; First 46RF Rem for the military, then 44 CF for military and commercial use. The Kirst is not original in the fact of being removeable, it is, but there never was a removeable conversion cylinder of the Kirst design. Kirst has a removeable recoil shield/firing pin assy, that is what is not original. The " 58 Remington converted with the Kirst Konverter and the ejector assy is a close copy of the original Remington factory conversions, not perfect, but very good. One can go to the trouble to fasten the Kirst recoil shiel to the frame with a shoulder screw or two and then this would be more historically correct.
The R & D is a bit more historically correct in the design with the multiple firing pins, and the Removeable cylinder and recoil shield/firing pins assy, not so original with 45LC(mfg after 1873) there were several (calibers) cartridge conversions with the R& D design, but not in 45LC until after 1873 and then only 5 shots. 45LC conversion of the R & D design were only 5 shot cylinders due to size restrictions of the cylinder dia. The R& D conversion is close to lots of original conversions.
So the answer is both and neither, just depends on how.jam uptight original you want to be.
I chose the Kirst Konverter in 44 Rem. to be as close to a factory converted Remington as one can get today and in an authentic cartridge for the Remington conversion Pistols and Colt conversion pistols in 44 cal.
I personally do not know how the R& D conversion cylinder shoots. I'm sure that the R & D will shoot very well in a gun that shoots.
I can attest to the Kirst and the gun I have it in. This thing will drive tacks when I get good enough to hold it more still.