I hear people calling their kits by names, if you bought from ebay, how do you know which motor you got? is it just head shape (round or square) or is there more to it.
I have no idea how many diff configurations are out there these days. If you read up a bit before ordering, you'll probably make a good choice. If not, whatever type you get won't run long anyway.
If you're talking about the stuff like "mustang" or "raw racer" or "flying horse" most of those engines are exactly the same, perhaps with a few components switched out, like the carb or exhaust pipe or the cylinder head, and with a fancy sticker on the side and the price raised a lot.