Have you run this engine? you showed us the exhaust port side of the sleeve, it can get discolored like that. for 15 bucks I'd try it out. do the bearings feel gritty? and does the front one leak?
If not use the same bearings, because once you start replacing bearings when other parts are questionable. then it's not worth it. the corrosion on the crank is typical of an engine that has sat a while, like a winter without proper maintainance or storage. But if you clean it well with break clean and use alot of after run oil before you refire it up. hell, even a 15 dollar pinch might help. 30 bucks to revive a motor isn't bad.