Have you not looked in the FSM and seen the different grade bearing shells and the #'s that match them?
Its real simple to determine what you need by looking at the #'s stamped on the side of the rod and block for rods, and the crank and block for mains.
I was also told by Sean Morris at RB Motoring that they are all so close in spec that you could really use any grade # in any rod or main and still be within spec of your avarage nissan motor.
The question is, do you want it to turn out "spot on", or will you accept "close enough"?