A buddy of mine saw on the SVT boards somewhere that the Nittos have a certain shoulder profile that ensures that if any brand will fit in a certain size, it is the Nitto. In the post the guy said he tried three other brands including BFG drag radials that all rubbed, but the same size Nitto 555 did not rub.
You gonna try the 555R drag radial, or the 555RII racing tire? I think the 555RII would be awesome, drag strip tread compound and a stiff sidewall for handling! Of course if it's a daily driver, it would get expensive- the tires don't cost THAT much compared to other brands, but you would probably be lucky to get 10 grand in mileage out of them.
Can you fit 275's in back?
About 7,000 horsepower... Many top fuel cars have speed density type EMS's. Oh in a 5.0 I hear there's 12 second SD 5.0's. If you can keep a good vaccum (no radical cam) you'll be alright. If I we're you mod around the SD and get parts that'll still function with MAF so don't go buying a SD cam unless you plan on staying with SD.
I have BFG DR 275/60-15's under the rear of my car. Fit great! Love how they fill up the wheel wells. I think the rims are 15X8 with a 5.5 BS. I might try a 9 or 10 inch wide rim in the near future for a better contact patch.