You can put nearly any engine in nearly any car. An NSX isn't any different. It all comes down to who did it, and how experienced they are, and how good of a job they did with the materials they had to work with. It's simply a car with a swapped motor.
Unless you know how to work on these cars, or have deep pockets to pay some one who does. You're taking a gamble. Bottom line.
No harm ment against the seller. It's just the nature of the beast.