The train in Poar Express was based on PM 1225.
You are correct — the engine and sounds in the animated movie were from PM 1225. However, American Heritage Railways/Rail Events is the Warner Brothers licensee for use of the name and music from the movie “Polar Express” and in turn licenses use for other railways (32 RRs for 2011). That is why the Michigan group uses the name “North Pole Express” instead of “Polar Express” for its Christmas trains.