Looks like a nice bike, but goodluck squeezing a engine(even a 48cc) in that bike frame.
It looks like a roadmaster sx sport mountainbike i use to have.
The bike frame or engine mounts may have to be modified.
You may have to make a cutom intake for you carb to clear the frame,either longer or off to the side. Your sparkplug may also have problems clearing the frame unless you get a slant head.
But if your willing to do extra work to get the engine mounted it looks like it would make a nice ride. But i bet there are easier bike frames to mount a engine on for around the same price or a little more.