Rich:
I was just going by Dan Wexler's afterword to the book [since I'm not that well versed in Prestwick's history], but I did not do a complete job. To quote:
" ... Charles Hunter expanded the layout to eighteen in 1883 upon the acquisition of additional land, and it was essentially that layout which was presented by Hutchinson. Remarkably, only two substantial alterations have been made in the 110 plus years since, the first being James Braid's adding of some 300 yards of length prior to the 1908 Open Championship (which he won). The second change was more substantial, however, for in 1922 the old seventh, a 193-yard par 3 was removed, allowing the angle and length of the par-4 eighth to be modified significantly. To replace the seventh, additional land was acquired to the northwest, allowing for the tenth to be extended from a straight 290 yards to a dogleg-right of over 450. The new eleventh, a 195-yarder to replace the seventh, was then routed back toward the south and right there, more than 80 years ago, our modern layout was set."
I know some of the 1922 work was by MacKenzie's suggestion; he was particularly harsh in his description of the new eleventh. However, most of the rest of the course (and pretty much all of the famous holes depicted in the book) are intact from 1883, if not earlier.