Look like a 45HP or a 55HP combine engine. The 45 are hard to tell from a 55 from the outside because the main difference is the bore. Different magneto brackets, and mags were used through the years but were interchangeable between the two engines. The engine in this movie has a Bosch mag on it and not the Splitdorfs used early on or the KW model HK (high bar) that most of us are use to seeing.
Thanks! I noticed one of the jugs was welded up too. Pretty cool to see an old Holt engine in a movie!