Mike indirectly makes a good point... such a good point he makes it twice!! :-)
There is a certain amount of variability with these cars, especially after 30+ years. What fits on one car might give you problems on another car - exhaust interference can be a problem on certain cars and not on others.
That being said, I'd make sure that your favorite wheel vendor allows you to return the rolling stock if you can't make it work for your application... there are horror stories about people with very expensive living room decorations now because they got the backspacing wrong, or because their car was not symetric, or...
Finally, as Mike says, I've seen rear tires of up to 345 wide crammed under a stock body...
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Charlie McCall
1985 DeTomaso Pantera GT5-S #9375
"Raising Pantera Awareness across Europe"
http://briefcase.yahoo.com/gt5s_1985