dynamis7

hi i have 03 gt with an auto and i want to know about transmission rebuilt i really want to do a transmission swap.. i had the thought of getting a manual gt trans from a junk yard and rebuild it the way i want... is this a good idea or would it just be better to invest in something like a tremec t-56.... but if it is a good idea what places or web sites could i get the correct gearing and transmission parts and what parts to get