I am looking to buy this Dunhill estate for Easter, but I am having a hard time identifying it and therefore putting a price tag on it. The only inscriptions it has are "R F/T" followed by "DUNHILL SHELL BRIAR" "Made in England" and "4S". From what I have seen on other Dunhills xS inscription and F/T relates to a 1960s series, but that most often comes with the inscription "Root Briar" not "shell" - although I have seen it with the "shell" wording as well. I haven't seen a 4S one for sale ... I guess that the 4 denotes the bowl size, as 2S and 3S all seem to be smaller in size. Any idea?