but you could probably get someone to fax you a plan by calling a local railroad engineering dept (CSX,Norfolk Southern etc.)
All #20 turnouts have the same geometry no matter the rail size. The only thing that may vary is the switch tie layout which will depend on who's railroad you are building on. Since this a number 20, I am assuming that you are tieing into a main or lead track, so you will need to comply with the railroads specs. Most competant builders will know what to provide if you specify the railroad.