After April 1963....all Single-Six Convertibles had both cylinders scratched with the last three digits of the serial number. The instruction manuals for these guns also stated if both cylinders of the convertible are not scratched with the last three digits of the serial number, or if those numbers are mismatched...do not shoot the gun" I don't remember the exact wording, but its in there. For guns shipped as single cylinder LR only (5-1/2") or Mag. only (6-1/2") it was standard procedure to not to have to take the cylinder out of the gun once it was fitted...there was no need to have to match that cylinder back up with the gun it was fitted to...you just leave the cylinder in and send it on.
The cylinder of your gun has numbers scratched on the front...the indication that it left the factory as a convertible. Also...even though there is one author out there that has written that single-cylinder RSS4W and RSS9W continued to be produced after the XR3 days and also says there were SC4, SC5 and SC6 LR only guns shipped, this is not the case. They were never advertised and it never happened.
I'll give a lifetime subscription of RENE to somebody who finds an RSS4W or RSS9W that letters as a LR only gun shipped after 1963, or even for an SC4, SC5 or SC6 that factory letters as an LR only gun. They don't exist except for the occasional factory "second" that pops up, or the LR only nickled Super Single Sixes that were shipped as cheaply as possible (with just one cylinder) just to get them out of the plant.
Chet15