That was an interesting link, Birdie Wife, on the thread in the Market Place, with reference to the Scots Dumpy breed, but surely those pictures are of Scots Greys.
I have once seen Dumpies and they were very low to the ground, with a very horizontal stature, and their legs could barely be seen as they waddled around, rather more like ducks than hens.
At one time, the scarcity of Dumpies was partly due to the problems the cocks had in treading the hens, due to the shortness of their legs.
Some breeders have used modern Greys in an attempt to recreate the old dumpies, and this is likey where the 'long-legged' types emerged from.
I believe the original Scots Greys were more of a gamefowl/utility type of bird. The old books show them as a lighter-built, more upright, active-looking bird than their modern, showbench counterparts. If one covers up the comb of the cock, in the old pics, the cock looks very like an Oxford gamecock. There were cock-fighting enthusiasts in Scotland as well as in England and Ireland, and I personally believe that some of them may have kept Scots Greys for the pit.
There are some colour forms of Carlisle OEG (those with part-barred plumage, such as 'creel', for example) which may have got some of their base genes from the old Scots Greys. Perhaps the Greys are an example of another breed ruined by showmen.