SHELBY GT 350 Member
Joined: Sep 2010
Location: see user name
Sounds like the O2 sensor bungs are mounted incorrectly. I've had no bad luck at all with BBK stuff (including the x pipe of theirs thats on my car), but this wouldn't be the first time I've heard of the bungs being positioned incorrectly on a BBK midpipe.
That was the long answer. The short answer is no; there should be no reason at all the your midpipe, it's O2 sensor bungs, or the sensors themselves should conflict with the x shaped brace beneath the car.
What part exactly are you unsure if you tightened all the way? The midpipe to manifold connection?
2001 GT Convertible
All the usual bolt-on's /200 I6, C4
And a few Explorers too... 2008 4.0 XLT 4x2, 1996 XLT 5.0 4x2, 2003 Sport Trac XLT 4.0 4x4