Blue the taper on your test bar, insert and twist. Now pull it out as gently as you can, pulling it straight so it doesn't bump around in the taper. Look at the contact pattern is it even, you might have to try this a few times. Like wise with blue in the head stock taper you can do again with the test bar clean.
You may already have witness marks on the test bar. If you do have a nick in the taper I would gently scrape it rather than hit it with a reamer.
Take readings along your test bar and rotate the spindle does the 8 thou gradually come in. Clock the spindle outer at the rear of the lathe, any runout.