I believe that some slop as you describe is normal.
When installed in the car, the tip of the input shaft is supported in the pilot bearing in the end of the crankshaft. Otherwise, it is supported by the input bearing, which by itself won't prevent it from deflecting from side to side, and a needle bearing where it engages the primary shaft.
Spin it by hand, in all gears, and feel for roughness. If it only turns smoothly in fourth gear, you may have a bad countershaft bearing.