Two of the same? No.

[Bikeguy Joe]

I Did a quick comparo on a couple of the Livefast Econo engines I have.

One has 14mm head nuts, one 10mm.
The first has 49.1cc's the other 47.4cc's. (due to a larger bore, same stroke). These are called "55cc" engines.

The casting on the jug is different and so is the bypass porting. (see photo 1).
The 49cc has straight cut gears, the 47cc has a slight helix to the teeth (think that's the right term, see photo 2).
The mufflers leave room for improvement, to say the least. (photo 3)