Papers to prove the km's, especially when it has a NISMO cluster in it, i'm not putting your car down in any way, just trying to help, but just saying it would help to sell the car if you had documents to support the Km's, i'd do a Japanese history check to obtain the auction sheet with the kms and sell that with the car, but if you choose not to its up to you.
Here's the link:
http://www.japanesehistorycheck.com/service/
GLWS