The Model 77 is made for a number of revolvers. I have a 77LS that is basketweave stamped and has the laced edge, and a couple more marked 77SS that are basketweave stamped but have no laced edge. It does however have a piece of leather sewn in above where an adjustable rear sight would rub. Maybe the SS means Sight protector, Stamped ? The markings for the guns are fairly easy to figure out, K6 will be for a 6" K frame S&W or of course others that are similarly sized. The 77SS holsters I have say R6 above 6 1/2 on the back and fits the 6.5" Super Single Six and regular fixed sighted Single Six models, and the other says N6. I haven't tried to see if a 6.5" N frame would fit that one but it does fit my 6" Model 57.
Does yours have an extra welt sewn in above where the rear sight would be ?