A plant in china - they are basically Honda Clones - same basic block and parts as an HF Predator or Husqvarna's own brand or the current LCT or Tecumseh/Lauson engines.. Even Briggs & Stratton and Kohler have some "low end" entry level engines built by one of the same factories in China.. Subaru Robin and Yamakoyo are other examples of these "similarities" - The price you are paying reflects the brand strength and warranty by each individual manufacturer.
The differences among the engines are factory spec for things like trim, intake and exhaust, etc. Another MAJOR difference among them all is the quality control process each manufacturer or brand applies to the engines that get their "badge" - For example, a Harbor Freight Predator engine might just be a visual check that everything's put together, box it and ship it.. so your odds of getting a "bad one" are more likely... other manufacturers may have specific quality control steps that need to be taken by the factory - and some even have their own "final finish" production lines where they assemble the engine from the bare block to their own specifications. But once you get them stripped down to the bare block they are all pretty much the same - You can generally go with Honda GC*** series (NOT GX series) of a similar displacement for internal specs - Parts are *sometimes* interchangeable, but there are many many *many* variations on things like carburetors, linkages, air intakes and exhaust systems - all are manufacturer specific engineering to meet EPA emissions requirements.. so a carb off a Powermore may look just the same as a carb off a Husqvarna or Briggs or Kohler or Predator version - but unless it is specifically built for that particular engine, it will likely not meet EPA Emissions requirements - so you may likely notice a great disparity in price strategy used by any given manufacturer since you won't be able to get that *exact* part from anywhere else.
But in the end, the basic block of the engine may be built by any one of a small number of production facilities in China... and they all have pretty much the same basic dimensions as the Honda engines they were originally cloned from.. Now that Honda's design patents are expired.
How poor are they who have not patience. What wound did ever heal, but by degrees? - Iago (Othello Act II, Scene 3)