Duncan,
Thanks for posting the very original MacKenzie sketch layout, fascinating stuff. I know this is seen through the eyes of a number of people who love Cavendish, but I suspect I'm not the only one that is seeing a layout that is quite poor in places? His 6th would have been a bit steep up that hill! Having said that, there is quite a bit there that survived to his next iteration that wasnt built, with 9, 8, 7 then 10 being his 1 to 4 by the look of it. Also the 5th in that sketch is pretty much the current 18th and the 17th in the original sketch is pretty much the current 10th. That would have made a great penultimate hole!
While the field in the north didnt become part of the course as you describe, they did manage to gain more land in the north west, as the original sketch doesnt have the land of the current 15th or most of the current 16th by the look of it. And only the 12th in the original sketch is on the embankment (about 14th green as currently is I'd say) with the current 6th tee, 5th green and 15th tee not within the original sketch red line.
Cheers,
James