Transformers found in Pine Valley build 55 or earlier. Possibly created by Rolf Mohr, as it was shared on his website.
This model was later modified to include the “Frankenstein Switch” puzzle, somewhere between build 55 and 96. The top bars of the power grid were also modified into one long bar (possibly in order to reduce poly count).

Source: https://web.archive.org/web/19991022053743/http://www.geocities.com/EnchantedForest/9057/Trespasser.html