X2 on piston slap.
Is it blown up? Well not yet. If there's a cast piston in there. If it is slapping it can break the skirt off the piston. Which often. Leads to case damage. I wouldn't run it. Till you check it.
If that's the case you should do as larry recommends and bore your stock cylinder.
Stay far away from those cheap cylinder,piston,head,carb kits.
When all that is cheaper than a weisco piston that should tell you something.