Good news on getting the registration updated. That'd be a big draw-back for most buyers.
That said, what's scary about the car is that all sat for 6 years. There will be a lot more wrong with it than just the waterpump / battery. The gas for example will be vinegar.
I'd just drop the price to $900k and get it over with. Or get the FIRM out of the ad. $600 is a good investment in your marriage.
G