speedo tooth recalibrator/speedcal question

[GreekStang85]

hey guys i am going to buy my gears soon and my uncle is a mechanic at ford and i told him that i want to change the gears and he said to order a speedo gear tooth, my question is does that work good for an 03' GT or do i have to get the speedcal?

 

[MachAzure]

Get the speed-cal from Dallas Mustang.