I don't have a ton of BB A-body experience, but the last one I did was a '67 Dart with a 440. I used the TTI 2" primary tube headers to a 3-1/2" exhaust. I was very pleased with the fit of the headers. I have the same headers for use on my '67 Barracuda. Good luck.
The TTI's are a great choice...just watch and read thier foot note...I believe no power steering a some instances no power brake booster and no column shift...I went the Schumacher way and if mine makes 500 hp then they are working for me...