You should have clearance on all your shimming, to allow for lubricant ingress, heat expansion etc.
Typically 0.04 - 0.10mm.
And you need to do this with the shell halves bolted up properly.
Once all gears are fitted, shimmed up, you should be able to whiz them round with your finger driving the sector gear.
Driving from the bevel gives you great mechanical advantage, in your case 12x as much
Aaaand check for tight spots during rotation, which could point to tooth profile faults, casting marks, burrs etc