I'm putting a spare 901 trans back together and everything went well until I tightened down the shift selector rod plate. When that's in the trans slightly loose, I can manually shift all gears but when tightened down, 1st and reverse only. The selector rod is not able to slide out to get 2nd & 3rd or 4th & 5th. Reading Red Beard's instructions...

"Slide the shift forks back onto the shift rods for and put the nuts and washers on loosely. Slide the shift fork alignment tool onto the gear stack. The shift rods can rotate slightly. Make sure that all three shift rod slots match up position wise.

Center each slider into the middle of between each gear set. Tighten the shift fork nut. 1st gear, adjust the shift fork so the slider is just off of the synchband for 1st. Tighten its nut."

So how does one confirm shift rod slots match up? Visually those appear aligned but somethings is definitely preventing the selector fork from sliding out.