This is a cool idea; I've never seen any fictional old-timey, early 20th century parks out there - the 1990s-00s retro parks don't quite work when used for that purpose, due to the buildings in the background being too modern, and there being much more seating all around the area behind the outfield walls than the old time parks had.
With a Create-a-stadium file I could strip those elements out. If a collection of skylines consisting of 1890s-1900s buildings were in the file, I could swap one in per park while keeping all the quirky-dimensioned walls of the modern retro parks (minus wall padding), and I'd have a pretty authentic-looking set of deadball-era parks without much additional work.
