Tom,
In response to your questions regarding the clubhouse, it has not changed locations though it has been expanded over the years but not toward the course.
With respect to the Zook property, it was acquired in 1919. I do not know the exact dimensions but it consisted of approximately 60 acres and almost doubled the club's then acreage to 160 (now approximately430). Zook maintained frontage on New Holland Pike. This is depicted in the routing posted above. Since we know that the lot fronting New Holland Pike was part of the original Zook Tract, my guess is that the tract extended to the southeast portion of the property (the road depicted to the left of the club property on the routing runs due east. The course is south of the road). I am looking into this question on the recorder of deeds site.
This routing is not entirely to scale and does not depict the topography of the property. I cannot say that this routing is the most ideal since it has changed considerably but there are only two spots on the course where the tee to green walk is not very very short. Existing 1 to 2 and existing 13 to 14. As depicted on the routing here, that would be 1 to 12 and the area of 17 green to 5. Other than some elevation change, Lancaster is a very easy walk.
As to your question regarding the dating of the routing, you are correct that on the face of the document it is impossible to know with certainty when it was prepared. There are factors, however, which strongly support the conclusion that this is the original routing prepared by Flynn.
First, Flynn's drawing style evolved significantly. The drawings I have seen from later in his career are more sophisticated and prepared on drafting paper.
Second, there is evidence to suggest that a portion of this routing may have been abandoned very early on. In the fairway on the current 13th hole there is an area where it appears that a green existed in the location of the 3rd green as depicted in the plan. Based on the way that this feature is carved out of a slope and knowing that it was farmland before golf course, there is no way this carve out occurred naturally. By 1927, however,holes three and 4 as depicted on the plan did not exist. Rather, 3 extended all the way to the northeastern corner of the property (upper left on the routing) and 4 was a par three that played from that corner to the area of the green as depicted in the plan. This is verified from the 1927 and 1940 aeriasl posted by Jim Nagle as well as other club resources.
Finally, a review of the aerials will confirm that the club did not implement a good number of the bunkering schemes depicted here. As I stated before, there was some level of skepticism of Flynn of a manner unique to Lancastrians! Roy Eshelman lamented that they did not give Flynn free reign to implement his plans to the fullest at the beginning of the relationship. It took 25 years of work by M. Eshelman and Flynn for the course to evolve as Flynn envisioned. So while the routing circa 1940 (pre crossing the river) was generally consistent with the plan with the exception noted above, Flynn ultimately abandoned many of the bunker arrangements depicted in the routing and went with others as seen in the aerials.