All the NP833 18 spline trannys I've work on, more than 3 , all had bushings inside the gears also.
NP offered multiple different gear ration in both the 23 spline and the larger 18 spline, The Blue Stripe 18 spline ratio was suppose to be very close to the early BB 23 spline ratio, the red stripe, I may have these ratio offerings backwards, had closer 2nd,3rd ratio for drag racing.
Are you going to drag race this tranny? If so the clutches offered today would probably work just as well on either tranny size saving you from spending money on the larger more expensive 18 spline parts
I've worn the sliders, brass and small ears off of both sets of 18 and 23 spline gears in the 2.65 and 2.66 ratio as well as the early A body 3.09 gear ratios
I switch from the stock Slick shifted gears to the Pro shifted gears and still had a lot of maintenance on them
I haven't ran any of the newer face plated gear sets, their suppose to be better and stronger than the slick and Pro shifted parts as well as your able to shift them without using the clucth