The most important thing is layshaft endfloat, this should be ~ 0.003"
Assemble just the lay shaft and its gears / spacers into the end plate and bolt up, check the end float with a clock gauge if you can, a crude test is a push / pull , 0.003" is just perceptible, if it clunks its too much, the spacing is set by the thick spacer that buts between the end gear and the drive side. or an accurate reading can me made by putting lead wire around the shaft between the end layshaft gear and the drive side . Bolt up to squish the lead, strip , measure lead thickness, subtract 0.003 , thats how thick the spacer should be.
Take an oil stone across the faces of all gears with dogs , stone off any raised burrs. This stop the gears trying to skip out as they enter the female dog holes. Same goes for female dog holes , stone off any raised burrs.
polish the face of the cam plate where the selector forks run. Polish the track of the cam plate plunger.
Cut two turns off the index plunger spring, if it hasnt been trimmed already. This makes the change a little lighter and more positive.