I have a Lenton Sports from about the same vintage. It's a lower end model than your Gran Sport, but has some similarities, such as the hi-ten steel frame. Some photos here:
http://www.bikeforums.net/showthread...=lenton+sports
The interesting thing there, and the reason I mention it, is that my frame has a completely bizarre braze on on the left chain stay. Someone suggested that it's for attaching a full chain case, which explains it pretty well, except for the glaring fact that this bike never had a full chain case and was never supposed to have one. Also bizarre is the oiler, just like yours except that it's on the RIGHT side of the BB. Could be that the Raleigh factory was just full of solvents, back then. Spec sheet? I don't need no shtinkin' shpeck seet....