Hello the park engine was a tweak off of a Randall Hudson so slightly smaller due to aluminum shrinkage.
There is also some small variation in the cab and cab window.
I was told 17 Park engines were recast..and sold as complete ? ..and 3 additional sets of castings made .
The park was initially advertised in 1946 or 1947 as a 3/8 of an inch scale Hudson virtually none sold
I'm fortunate to have a pair of the Randall Hudson's in standard gauge and one built up in one gauge, but no Park engine yet.
Here is a video link to see the Bob Hendrich built Hudson and Berkshire ..both using the Randall Hudson boiler.