I would grind the teeth off of the 1st gear brass and shorten it so I could shift into 1st. gear with a stock 1st. gear (don't have it modified ) after the run without shutting the motor off.
Never shift it slowly with the car moving also, quick, speed, shifting it racing or driving it back to the pits or in the pits going to the staging lanes
If I was building a NP833 today I would have it face plated, not Pro Shifted