I went to town today and went to this store to get some Tygon line . . . .
http://glenssurplus.com/products.php?cat=471

I saw four new - four stroke engines there. No Carb, No muffler, No flywheel or ignition system $15 ea

They looked like wacker engines to me. You will have to call and ask?

These engines appeared to use a 10mm plug but the threads are deep.

These short blocks are more than likely Ryobi's as there are several MTD plants in this and surrounding cities.

They are push rod engines