All the advise you are getting is correct. The motor will have casting numbers that cover a longer range of time that they were used on cars. There were no VIN's stamped on the earlier engines. Th price being too high or too low really depends on whether you want to pay that much. If it is a complete car that you are going to work on to make into a nice driver and you have all the parts, it needs little or no body work, runs and drives, the $3995 may be a decent price if you can get out and enjoy your investment in a car you really like. If you are planning to toss some money around with the expectation of making some money when you sell it, that is not likely to happen.
If you look at less expensive ones that are going to require searching for parts, redoing things, rebuilding engines/trans, body work, and consider the amount of time it takes to do all that, the one you are looking at still sounds like a decent deal. However, if you want to get one that you are going to build yourself, this is a mute point.
Simply put: If you like it, want it, have the money for it (and you aren't depriving your family to do so) then I'd say go for it. They are NOT making any more of them!