I have a 1988 GT and the only modification that I have done so far to this car is put a 2.5 inch off road H pipe with Flowmaster 40 series mufflers. I am new to modifying Fox's so and am interested in getting some long tube headers. I'd like to go with BBK but based on my setup I'm not sure if I should get 1 3/4 inch or 1 5/8 inch long tubes. The car was bone stock when I first bought it. Thoughts?