#2 morse is correct for the tailstock. The tailstock ram is pretty short, so a full length #2 will only grip with the ram extended about an inch. Just use a cut off disc in an angle grinder to chop the end off that new chuck adapter you buy. You want it to just eject before the tailstock is fully retracted.
Try to get the shortest chuck you can find. The 7x10 doesn't leave you much room.