MRacer,
Sounds like you have gotten really good advise and your cousin should really be able to help with this one. One thing is, if you see an NSX valve you will know they can easily be bent and not necessarily ruin a piston. These babies are tiny and fragile!
Even looking at the valve stem diameter is a give away. Steve mentioned looking at the valve clearances, the way to go, IMO also. You can additionally look at the relative valve height, cylinder to cylinder, to see the same thing, with a reference.
In regard to a new motor vs. a rebuilt or replacement, I personally feel this is an economic decision. I would not exclude either way, until you finish shopping.
A used engine with low mileage, may just be a better deal. Now if you can somehow get free labor (your cousin must be cursing you out by now) the tear down and valve replacement may be more cost effective.
The other thing to consider is with any teardown, and this is NOT a chevy V8 with push rods, there is some risk.
If you did it all day, it's easy, but I do not know too many folks that do NSX engine rebuilds all day, even trained NSX techs!!!!!!
My whole point here is really think this all through, do your homework (read$$) before you rule out one way or the other.
HTH, My $.02
LarryB