I wouldn't expect a miracle from the bicycle kit. A moped is a small motorcycle. Everything is bigger and heavier. Aside from the displacement moped engine components are built thick and strong, everything from the engine block's mounting bosses to the connecting rods and bearings.
Swapping the original motor with something that was never designed to be in a moped will be far more difficult than would be restoring the original.
At first your bike might seem like too much to handle overall, but once you get into it you will find that there is not all that much to these little bikes. Carbs can be purchased and wires can be replaced. The worse the shape that your bike is in, the more you'll learn and the more satisfaction you'll get from restoring it.
I found my first bike in a metal scrap yard. It had been run over by a large earth-mover. The bike had been generally crushed.. the frame bent to an "L" shaped. A month later it was on the road..