Something was wrong if Dougs or tti don't fit, like engine in wrong spot, etc. Could be you got the wrong header. that's happened with both tti and dougs before.... stuff happens
however something is wrong with alot of these cars its incredible that some companys actualy manage to make anything that fits good on most of the cars considering the hopeless tolerances these cars have from the factory. these old american musclecars are all over the place when it comes to tolerances and they sure didnt get better over the years. and yes that goes for most all of them regardless of brand.
