The stock TB is 66mm at its widest point, the afermarket TB's are 65mm at the butterfly. Personally I would get an aftermarket one. You can "port" the stocker BUT it still doesn't change the width at the butterfly.
Honestly i would hold out on the TB for now. For the cost there are some better mods that you can do. I was a huge fan of larger throttle bodies on my old Lebaron V6. They came with 46mm TBs and you could go to the junkyard, grab a 52mm TB from a 3.3L mini-van and it was a HUGE improvement.
I was quite upset with how little improvment the 65mm TBs has on the SVT. Me thinks the intake path is not much if any of a restriction, atleast not until you hit some heavy modding.