BUY IT STOCK!!!!!!!!!! You Never know why it's being sold. The last guy may have used an OLD crank bearing he Hammered in with a rock. You NEVER know what was done.
If you are Not familar with a total build then buy one of those old Dio's and practice first. A few hundred (300.00) bucks will get you some needed tools, and the experience to Know how to put it together. Same in the US if I were to buy an '02 Mina engine Aprilia for 1,000.00 bucks, and spend 1,500.00 on TOP shelf parts... I know what was done. OR I could but a used pre-built pile of sh** for the same money.,
Build one yourself. If it fails... You may still be able to re-use most of it.