All I can say is 2 1/2 tailpipes are very tight but doable on a 67 B Body in a stock location. I had a set on my 67 Coronet from Don's Custom Exhaust.
Were they press bends like any muff shop or mandrel... I'm talking all mandrel bent exhaust... press bend you lose 15% per bend... thats why MOST all production exhaust is mandrel bend... aftermarket... different world