Personally I'd never buy an engine without seeing it running first, no matter how much the seller says he's not a con man and especially as he has no proof the engine has done 60k.
Also you'll need more than just the block, head and box. Your best bet is to buy a VR6 donor car that's had an accident from behind and get all the bits off that as not only will you be able to see and hear the car run but you'll be able to get all of the bits needed for the conversion. (it's not just engine, there's wiring and clutch parts too as well as hoses and ancillaries).
Oh and set your budget higher as once the engine is out you'll want to change various gaskets and on a VR6 especially, the timing chain.
