Remove the cross pin access cover . Insert a 3/16 cross pin, or 3/16 drill bit , into the hole. It will sit just under the motor shaft and will push against the coupler to set the preload of the transmission shaft.
Thread the 5th axis assembly onto the HA5C nose. Use care to get the transmission shaft  piloted back onto the motor shaft.
Tighten the (4) set screws  on the adapter. Install the (4) access cover plugs .
Tighten the motor coupling bolt and install the access cover.
Note: If the motor coupler is no longer aligned you can remove the front cap  and rotate the worm gear to correct the alignment.
Remove the cross pin, or drill bit. Leave the access plug out to refill with oil.
Install the drain and fill plugs.