You need 17" minimum up front to clear the brakes. You can go 15 or 16 in the back (look up Bogarts). However, why not just get a set of take off wheels from a stock GT? For just a few hundred buck + the drag radials of your choice out back, you've got a bargain set of wheels/tires for the track. That's the route I went. Of course, you could do a set a Bogarts (big & littles) and spend $2K, $3K, or more for the set up.
Just get some take off wheels (17") from a GT and put some 275s or something on that. I believe the stock 17"s were 8.5" wide right? Which is right where most vendors say.
What kind of tires were you looking at getting? Radials or slicks?
You can get a set of bullitt type gt take offs with tires [mt et streets] for $650 complete from Brenspeed. Wheels are factory take offs with less then 1 mile on them,tires are brand new of course. Wheels are 17" tires are 10.5 x 26 and fit the wheels perfectly. They come unmounted ,about 20 per wheel mounting cost any good tire shop.