For the current value of the car, not very much. I would say you'd be quite lucky if someone gave you $1,000 for it. Unfortunately it's a very big project to try and restore, and by the looks of things every panel has rust and/or panel damage. A lot of time, money and effort would need to be put into restoring it, and as a realistic value on the car restored, I would estimate at $5,000-$6,000. If you're wanting a 200B on the road, you would be best trying to find a clean shell and then swapping the driveline and interior from your current car into it.
The spoiler is definitely not from a Datsun, but the milage may be correct - only the Japanese and SSS clusters go up to five digits, the Australian-delivered clusters go to six digits. That said, it's not uncommon for the odometers in 200Bs to stop working, so it may have got stuck there.
I don't know what you paid for it, but your best financial bet would
probably be to part the car out. I'm a bit out of touch on the value of a lot of these parts, but if the engine runs well that would be worth a bit, same with the bumpers if they're in good condition. The front end is worth a bit too, and you may find someone who wants the interior.
_________________green200b - aka Alistair
'80 200B GX - the green200b
- hibernating indefinitiely
'81 RX-7 - 12A extend port, 4.375 LSD - daily (currently hibernating)
'74 RX-2 - 13B bridgeport, 4.444 LSD - cruiser (also hibernating)
Green200B has forgotten more about 200Bs than we will ever know.