I ran a liberty proshifted A-833 years ago. Most slick shifted transmissions were done by the racers, you just grind off every other tooth, on the synco and brass ring. give a bigger window to hit at high RPM. The proshifted transmission had the synco teeth cut off and a lug ring welded in place. You had to shift them hard and fast, or you would burr the lugs, and that was the only maintenance I normally did every season pull it apart and file the lugs square. I used a inline 4-speed and the car was one of the few manual transmission's bracket racing that did any good. The car only weighed 2,2300lbs so it seldom broke anything. It was a 340 4-speed I took out of my 1979 dart and dropped in the Anglia.
But you just shift them fast and hard.