nice image, Jim -- illustrates my words perfectly.
Ken,
Yes, at Great Coxwell the height of the post feet up on those stone columns would have necessitated the entire Xframe be built on an elevated scaffolded platform and then the raising posts inserted in the now empty mortises, the ropes run over the top and dozens of oxen or hundreds of men or some pretty large windlasses or all of the above would be ready to take the strain and up it comes slowly....
I would really love to go back in time to see those massive cross-frames being raised.