My 16", 1937 Southbend is a 'coaster'. One reason the chuck has never unscrewed in reverse.
My homemade holder gets up close to the shoulder, you can under cut the shoulder if you like.
I only do light cuts when threading.
My brother has a 16" 1956 quick change.[Southbend] He bought several gears and can cut nearly all metric threads.
16" are cheaper than 10s. Mine will do 56" between centers. Works very well for me.
