[tbirdtbird]

You can crack a hub if you are not careful on this.
On every tapered axle I have ever worked on (tons over the years, all makes) I put the taper in and down, since the broached slot ends in a taper.
I only partly start the key, install the hub carefully, get the hub all the way on, and some of the key is still protruding. Then I put a small screwdriver on the key and gently tap it inboard until flush with the hub, allowing of course for the special 5/8 grease seal. This way I know exactly where that key is and I am satisfied that it is not inboard too far, 'cause if it is you won't be able to tighten the hub properly and also run the risk of splitting the hub when you go down the road.

I only wish Henry had made the threads 3/4 inch like all the other makes I work on instead of 5/8; 3/4 inch would have stood up better to all the torquing that goes on over the years. Lots of stripped 5/8 threads out there.

Anyway it works for me.