As long as there are no dings, scratches, foreign matter, etc., I have always warmed up the chuck just a bit in a toaster oven for a few minutes, and or put the arbor in the freezer for a few minutes first. Then gently seat the tapers together and give the arbor a good, firm rap on the tail end with a brass hammer, or at least slam the R8 end down against a wooden bench. With only a few degrees difference in temperature, they will have a firm grip when things equalize. If the tapers are clean, there should be very little runout.
If you have to clean any dings, etc off, be sure and do a uniform job. It's a little harder to get them back apart if you assemble them as I described.