The late model R32 (Kouki) had a number of minor changes, including the larger oil pump drive on the crankshaft. Other obvious changes were a smooth rear diff backplate (finned on the earlier Zenki model) also the clutch release was changed to a pull release a la R33 GTR. If your car has either of these mods then it will have the revised crankshaft. The collar you mention is an add on to update an older model crank to the bigger oil pump drive. Jun do them as do Abbey motorsport and Rising sun Performance. How I fit them is:- Inspect crank first, then turn the original pump drive off so there is a 0.075mm (3 thou) interferance fit with the collar. Heat the collar and cool the crank in liquid nitrogen, then press the collar on. Drill and tap the flats to fit the supplied grub screws, clean up and re-check, job done, or you can just buy a new crank from Nissan, they are £900!!!
I have just measured the flats on a deceased R33 crank I have here and they are 18mm in length front to back. The Earlier crank is about 8mm. The contact area on the small pump drive is only about 3mm, you can see where the contact has been. Scary really when you think about the load on this small area!!!
Check my thread, I had to have a collar fitted, also theres a pic of my old pump gear that shows just how little contact area there is on the early crank.
Ps you dont have to remove the oil pump to see if you have the early crank but you do have to remove the lower pulley, cambelt, crank sprocket and front main oil seal and you will be able to see the drive.
Make sure the N1 pump is genuine. However couple of things you should think about - how much power do you want to push out of this engine and what kind of crank so you have at present.
If you have a narrow drive early crank the contact patch would be very small and would not recommended high revs or banging on the limiter ie launch control or bee rev limiter etc. Also if you have the wide crank the same would apply as long as you take it easy.