Not until the last decade or so have I fitted any gearbox in the manner that I do now. Ultimately, I find this method saves time, especially with regard to setting the correct running clearance of 0.003" to 0.011(?)" (or whatever the maximum is, which I never settle for
)
Firstly, just the gear cluster alone with the endplate, it's fastening & dowels, to check that it freely rotates, & whether it may require any or no shimming @ the needle bearing end. It's debatable as to whether a shim is mandatory for the needle bearing end & often, in the case of homemade close ratio 'boxes there may be a weld/braise radius that does not allow one to be fitted. Otherwise, it's best to shim to control the bearing float & keep the needle in it's designated area.
Secondly, as above but just all loose gears alone (with endplate etc but no cluster!) for clearance check to precisely 0.003" using the collection of size engraved shims that I have amassed, many refaced on a surface grinder. This may involve swapping of end plates (never had a problem with that principle) or changing the bearing bush within. Obviously, the hub nut needs to be torqued up, often just with spacers if need be. This process also serves to show up any deficiencies in the sliding cursor, which is far too common with the cr@p replacements available, but another subject in itself
Lastly, fit the whole assembly which should spin up nicely. However, it is worth ensuring the best possible edge alignment of the gears by being prepared to shim up the cluster just under the endplate. Fussy, I know, but those gears of ours are not very wide & sometimes the cluster can pull up
too far