I never heard for a single crank on a V4 NSR.
As i know all of them have two cranks with the same design like this in the photos.
A think that i remember and impressed me when i saw it,was that the NSR500 V4 after 1989 models as it is this in the photos has a specific design on the cylinders to prevent more coolant after some problems with the temperatures.
This design almost doubled the coolant amount of the cylinder and the head studs actually been outside of the cylinder.
If you are interesting i may have a drawing of it somewhere in my pc folders,just let me know to search for it.