hello steven, welcome to SBF!! you could measure the length of the crankshaft and head to harbor freight to see if the 301 or larger motor is the same lengthdo the same with a briggs too. you could look for another hm100
Generally speaking, pay attention to the shaft diameter--they are usually either 3/4 or 1." Can use a sleeve to enlarge a 3/4" shaft. The two Tecumseh frame sizes you can encounter have the same mounting bolt pattern but in a different location. I think most blowers will be drilled for both.
Cheap as they are, the Harbor Freight engines are a more modern and sophisticated design. They will generally have compatible mounting and shaft dimensions. But, few people are going to run a snowblower enough hours to wear out a properly maintained engine.
In some cases, an overhead valve engine may have interference with the chute control.
If buying a Briggs or Tecumseh, "cast iron sleeve" or "Industrial/Commercial" are very desirable.
Of course, you know that snow engines have differences including no air filter, baffles to keep more heat around carb and governor linkage, large pull rope handles.... You can convert one to the other, but be aware.