Good idea, check with Wayne & Son first for verification. If they can't remember the bike or motor - and that would surprise me - have him pull the valve cover. For 3 grand into the motor, you should see things like aftermarket retainers, stainless valves, slotted sprocket, lumpy cam. Get the aftermarket markings off the cam - not just casting numbers. Look down the intake ports for signs of porting. If he balks at this move on, what's the problem with removing 5 minutes of cover bolts to prove to a potential customer he's getting what's advertised?
Look closely at the head gasket, is it copper? That alone is a very good indicator it's kitted. If it has this stuff done, it may be a good bet that he's telling the truth about the Wiseco kit.
Does the motor come with an aftermarket ignition, coils, different carbs? These are the things that add up in value. Ask if the tranny's cut, crank balanced, alternator lightened, stud kit, etc.
These are the questions that can give you some insight as to what he's really got.
You could be onto a real find - just be careful... And good luck.