The accuracy is dependent on your 8-track. Is it digital or tape (tape will stretch, motors are not entirely accurate, etc.)? The longer the song the more chances of mis-alignments.
You may have better luck at transfering the tracks then putting on the grid in N-Track and chopping each track into shorter phrases with an audio editor and then lining everything back up manually.
(When I work on a song in N-Track I tend to work in 4 or 8 bar phrases anyway.)
