I just posted a couple of pics of this one in the gallery this morning. Had I seen this thread first I would have put them here. Picked this one up at the Hoover, Alabama show a few months ago. T. A. here helped me with the #8 Tyler, perfect for this little snubby.
GA-36HT FBI National Academy 50th Golden Aniversary commermorative together with a "blank canvas" ordered by the engravers, prepared by Ruger, but not engraved.
Notice the lack of the roll mark "Ruger Security Six" below the cylinder window on the frame and the "fat letter" "RUGER" on the barrel. This is the first use of this barrel roll mark which then was used a very short time later on the new GP100.
A couple of "uncommon" short barreled Service Sixs - SDA-82 in .38 Spl. and SDA-32 in .357 Mag. Most of the short barreled fixed sight six series were ordered with round butts as the Speed Six.
Notice the scalloped vis non-scalloped frames and the later, heavy barrel profile on the SDA-82.
RDA-86 and RDA-84 "low back". The .38 Spl. are uncommon, even rare, in the adjustable sight models of the Six Series. Maybe a little as 5% of production. It's estimated that there may be fewer than 500 blued 6" adjustable sight .38 Spl. low backs. The 4" are more plentiful, but still "uncommon".