Steve, you can seat it by first cleaning the taper and inside of the chuck with alcohol or lacquer thinner. Then freeze the taper in the freezer for a few hours. I then heat my chuck on top of my radiator shop heater that gets to about 200 degrees to heat it up.
Once everything is at temperature, put the chuck nose down on the bench (gloves-its hot!) and the drop the cold taper down into it. I give it a tap with my small brass hammer to seat it a little further.
Let the temps come back to normal and it should stay put if you don't abuse it.
I'm not sure this is the 'approved' method for this piece, but this is how we seat tapers in machinery at work, so I used it on my chuck.
PS- don't put a cold taper into your lathe head/tailstock!