I did the AN lines MANY MANY Moons ago but I think at least one of the lines on the trans required an AN adapter that looked like the one in the PIC, a Straight Mechanical Pipe Thread with an O-Ring to -6 AN.
For some reason I am thinking it was just one of the lines - maybe the upper fitting in the trans case that possibly already has a brass adapter fitting that takes the O-Ring fitting???
trans case fitting is 1/4 npsm ..and u get a copper crush sleeve for the 1/4 side before it was nylon . i do this to all my buicks after i get a Janis trans built .. -6 line with a derale trans cooler with a fan on the front