150cc Hexagon engine condition? Full of rust

Someone offered me this 150 lc engine from a hexagon, says it has like 5000km but it needs cleaning because its full of rust since he just had it stay for a long time. What do you guys think of it? Is it all fixable and cleanable (the rust), and how can i clean it.

 

It appears that the engine has been left open for a good while.
Personally I would strip it completely, split the engine halves, clean and check everything, replace where necessary.
The barrel looks like it would clean up with a quick hone, as long as there are no scores down the bore should be fine.