Downunder has illustrated the basic 'slider" type adjustable leadout guide. I make my slider out of 1/8 ply with a blind nut for the holding bolt and use the golden-rod type yellow plastic tubes, about 3/8 long, for the leadouts to go through. I glue them in with thick CA. Get the leadouts as close together as you are comfortable with. Separation will generate yaw when you give control one way or the other. On a 1/2A size airplane, I like both leadouts to come out one hole.

Where adjustable leadouts help you is when you have good line tension down low, but poor line tension above 45 degrees. This can be corrected by moving the leadouts forward. Move them about 1/8 in at a time until the airplane pulls to suit you. If you get them too far forward, the airplane will yaw in when you hit a hard corner.